Terminal and communication method

ABSTRACT

The present disclosure aims at allowing a demodulation reference signal (DMRS) pattern suitable for a terminal to be selected from among a plurality of DMRS patterns including Legacy DMRS and Reduced DMRS. Disclosed is a terminal including: reception section 21 that receives uplink control information; control section 23 that determines a specific mapping pattern from among a plurality of mapping patterns for an uplink DMRS on the basis of the control information; and DMRS generating section 24 that generates a DMRS according to the specific mapping pattern.

BACKGROUND Technical Field

The present disclosure relates to a terminal, a base station, a methodof generating a DMRS, and a transmission method.

Description of the Related Art

Long Term Evolution (LTE) Release 8 (Rel. 8) that has been standardizedby 3rd Generation Partnership Project Radio Access Network (3GPP) hasadopted single-carrier frequency-division multiple-access (SC-FDMA) asan uplink communication scheme (see, Non-Patent Literatures(hereinafter, abbreviated as “NPL”) 1, 2, and 3). SC-FDMA provides a lowPeak-to-Average Power Ratio (PARP) and high power usage efficiency forterminals (User Equipment (UE)).

In the uplink of LTE, both data signals (Physical Uplink Shared Channel(PUSCH)) and control signals (Physical Uplink Control Channel (PUCCH))are transmitted in units of subframes (see, NPL 1) FIG. 1 illustrates anexample of a PUSCH subframe structure in the case of normal cyclicprefix. As illustrated in FIG. 1, one subframe consists of two timeslots, and a plurality of SC-FDMA data symbols and pilot symbols (whichis called Demodulation Reference Signal (DMRS)) are time-multiplexed ineach slot. Upon receipt of a PUSCH, a base station performs channelestimation using DMRSs. The base station then demodulates and decodesthe SC-FDMA data symbols using the result of channel estimation.Incidentally, Discrete-Fourier-Transform Spread Orthogonal FrequencyDivision Multiplexing (DFT-S-OFDM), which is an extended version ofSC-FDMA, has become available in LTE-Advanced (LTE-A) Release 10 (Rel.10). DFT-S-OFDM is a method that expands the scheduling flexibility bysplitting the PUSCH formed as illustrated in FIG. 1 into two spectrumsand mapping the respective spectrums to different frequencies.

DMRSs to be multiplexed with a PUSCH are generated on the basis of aConstant Amplitude Zero Auto-Correlation (CAZAC) sequence excellent inautocorrelation characteristics and cross-correlation characteristics.In LTE, 30 sequence groups each formed by grouping highly correlatedCAZAC sequences having various sequence lengths (bandwidths) are defined(see, e.g., FIG. 2). Each cell is assigned one of the 30 sequence groupsaccording to a cell specific ID (cell ID). As a result, the cells arerespectively assigned sequence groups having low correlation between thecells.

A terminal generates a DMRS using a CAZAC sequence corresponding to theallocated bandwidth in the sequence group assigned to the cell servingthe terminal and multiplexes the DMRS with a PUSCH. Accordingly, highlycorrelated DMRSs are transmitted from terminals in the same cell whilelow correlated DMRSs are transmitted from terminals in different cells.Even if interference between DMRSs transmitted at the same timingoccurs, the interference can be reduced by the window function method orequalization because of the low intercell correlation of DMRSs.Meanwhile, the terminals within the same cell can be operated withoutinterference by allocating different frequencies or time to theterminals for orthogonalization. In addition, the same frequency or timecan be allocated to different terminals (which is called “Multi-usermulti-input multi-output” (MU-MIMO)). In this technique, DMRSs ofdifferent terminals can be orthogonalized by configuring a differentcyclic shift (CS) for each terminal or multiplying two DMRSs ofterminals on a PUSCH by different orthogonal cover codes (OCC).

As described above, the reduction of intercell interference usingdifferent sequence groups achieves spatial recycling of radio resources.In addition, application of MI-MIMO enables using radio resourcesefficiently within a cell. In the manner described above, LTE enableshighly efficient uplink transmission.

Furthermore, vertical cell IDs, which enable allocation of any sequencegroup to any terminal regardless of cell ID of the serving cell, areadded in in LTE-A Release 11 (Rel. 11).

Incidentally, there has been an explosive increase in mobile traffic dueto the widespread of smartphones in recent years. Thus, significantimprovement in use efficiency of radio resources is required forproviding users with stress-free mobile data communication services. Inthis respect, small cell enhancement, which involves deployment of aconsiderable number of small cell base stations each forming a smallcell, has been studied in LTE-A Release 12 (Rel. 12) (see, NPL 4). Smallcell enhancement is advantageous in that the radio resources allocatableby each cell per terminal can be increased by reducing the coverage toreduce the number of terminals per cell and that the data rate ofterminals can be improved accordingly. Meanwhile, it is unrealistic tocompletely cover all areas by small cells. In addition, another problemis that the frequency of handover increases when a high-mobilityterminal is connected to a small cell. For this reason, small celldeployment under the coverages of macro cells, each providing a largercoverage, in an overlaid manner has been considered (see, e.g., FIG. 3;sometimes called heterogeneous network (HetNet)). This small celldeployment enables providing large-volume communication to low-mobilityterminals in need of a fast data communication service in small cellswhile eliminating coverage holes and supporting every terminal in macrocells.

Citation List Non-Patent Literatures NPL 1 3GPP TS 36.211, “EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical channels andmodulation,” v.11.1.0 NPL 2 3GPP TS 36.212, “Evolved UniversalTerrestrial Radio Access (E-UTRA); Multiplexing and channel coding,”v.11.1.0 NPL 3 3GPP TS 36.213, “Evolved Universal Terrestrial RadioAccess (E-UTRA); Physical layer procedures,” v.11.1.0 NPL 4 3GPP TR36.932, “Scenarios and requirements for small cell enhancements forE-UTRA and E-UTRAN,” v.12.0.0

BRIEF SUMMARY Technical Problem

The network configuration that has been studied in small cellenhancement (see, e.g., FIG. 3) has the following characteristics.

(1) The channel condition and quality for terminals connected to a smallcell are typically good. This is because the distance between a smallcell base station and each terminal is likely to be short, so thatcommunication is likely to be performed with higher received power orhigher signal-to-noise ratio (SNR). In addition, the transmission powerrequired for terminals is likely to be low for the same reasons.

(2) The number of simultaneously operated terminals in a small cell issmaller than in a macro cell because of the smaller coverage of smallcell. A small cell may even communicate with only a terminal or two.

(3) Unlike macro cells, small cells are unlikely to be deployed evenly.Small cells may be deployed locally densely, while they may be deployedsparsely in a wide area.

According to the characteristics described above, it is expected thatbase stations can perform sufficiently accurate channel estimation sincechannel states and quality are good in the uplink of terminalscommunicating with small cells in small cell enhancement. Meanwhile,since the number of simultaneously operated terminals in each small cellis small, an advantage of application of MIMO is reduced. For thisreason, it is not always necessary to use 14% or more of a PUSCHsubframe ( 1/7 of the total) for DMRSs as illustrated in FIG. 1.Specifically, higher terminal throughput can be achieved if DMRSs in aPUSCH subframe are reduced, and radio resources thus obtained by DMRSreduction are used for data (PUSCH) for uplink communication ofterminals with a small cell.

Because of the background described above, application of a techniquethat improves the data rate per terminal and per subframe throughreplacement of part of DMRSs on a PUSCH with data (the technique isreferred to as “Reduced DMRS” in the following description) has beenstudied in small cell enhancement. For example, if the DMRSs included ina PUSCH subframe illustrated in FIG. 1 are reduced to half, the datarate can be improved by approximately 7%, and if the DMRSs are reducedto ¼, the data rate can be improved by as much as 11%.

FIG. 4A illustrates mapping pattern indicating DMRS (Legacy DMRS)mapping in a single subframe (legacy DMRS pattern) in Rel. 11 or before.FIGS. 4B to 4E illustrate exemplary mapping patterns each indicatingDMRS mapping in a single subframe in Reduced DMRS (Reduced DMRS patterns(1) to (4)). As illustrated in FIGS. 4B to 4E, the proportion of a DMRSin each reduced DMRS pattern is less than in the legacy DMRS pattern.Stated differently, the resources to which a DMRS is mapped are in theReduced DMRS pattern is less than in the legacy DMRS pattern.

The legacy DMRS pattern (see FIG. 4A) corresponds to a subframestructure illustrated in FIG. 1 and is a pattern in which two DMRSs aremapped in a single subframe.

Reduced DMRS patterns (1) and (2) (see, FIGS. 4B and 4C) are each apattern in which one of two DMRSs included in the legacy DMRS pattern(see, FIG. 4A) is replaced with data. As a result, application oforthogonal cover codes (OCCs) becomes difficult, but the data rate canbe improved by increasing the amount of resource allocation to data. Inaddition, when PUSCH subframes of reduced DMRS patterns (1) and (2) areconnected together temporally and transmitted contiguously, two DMRSscan be used over two subframes, so that multiplexing by means oforthogonal cover codes is possible (see, e.g., FIG. 5A). Likewise, whenthe PUSCH subframes of reduced DMRS patterns (2) and (1) are connectedtogether temporally and transmitted contiguously, two DMRSs can be usedover two subframes, so that multiplexing by means of orthogonal covercodes is possible (see, e.g., FIG. 5B). Moreover, since the temporaldistance between DMRSs multiplied by orthogonal cover codes is small inFIG. 5B as compared with FIG. 5A, it is possible to apply MU-MIMO to ahigh-mobility terminal.

Reduced DMRS pattern (3) (see, FIG. 4D) is a method of mapping DMRSseach having a sequence length shorter than the allocated bandwidth in adistributed manner in each SC-FDMA symbol. As in reduced DMRS patterns(1) and (2), the data rate can be improved by allocating the resourceelements (RE) to which no DMRS is mapped to data. Moreover, orthogonalmultiplexing of DMRSs between different terminals by means of orthogonalcover codes is possible as in the case of Rel. 11 (FIG. 4A) because theconfiguration in which DMRSs are respectively mapped to two differentSC-FDMA symbols within a single subframe is maintained in reduced DMRSpattern (3). Accordingly, reduced DMRS pattern (3) is advantageous inthat application of MU-MIMO is easier. Meanwhile, reduced DMRS pattern(3) has a concern that PAPR of the terminal increases, considering thata DMRS and data are frequency multiplexed in the same SC-FDMA symbol.However, since the transmission power of a terminal connected to a smallcell is likely to be low, an increase in PAPR of the terminal does not amatter. In addition, the resource element to which a DMRS is mapped inone of the two SC-FDMA symbols may be shifted from the resource elementto which a DMRS is mapped in the other one of the two SC-FDMA symbols(not illustrated). In this case, the channel estimation accuracy can beimproved by averaging or interpolating the channel estimation values bythe DMRSs included in the two SC-FDMA symbols.

Reduced DMRS pattern (4) (see, FIG. 4E) is a method of locally mapping aDMRS having a sequence length shorter than the allocated bandwidth ineach SC-FDMA symbol. Reduced DMRS pattern (4) is advantageous, ascompared to reduced DMRS pattern (3), in that channel fluctuations inthe frequency direction in the band to which the DMRS is mapped can beeasily estimated, and that the effects obtained in reduced DMRS pattern(3) can be also obtained. It should be noted that, the frequencypositions at which DMRSs are mapped, and the relative frequencypositions of the DMRSs between two SC-FDMA symbols are not limited tothe example illustrated in FIG. 4E.

Some examples of Reduced DMRS have been described above.

However, it is not true that Reduced DMRS is always effective. Forexample, Reduced DMRS is effective when the channel quality of aterminal is good, but when the channel quality is poor, it is preferableto increase the channel estimation accuracy by increasing the DMRSenergy using Legacy DMRS. In addition, when large interference from aterminal to a neighboring cell is expected, the use of Legacy DMRSrequires keeping the correlation of interference to the DMRSs ofterminals connected to a neighboring cell low. Moreover, it is necessaryto use Legacy DMRS for terminals supporting the features of Rel. 12 whenMU-MIMO is applied to terminals supporting the features of Rel. 12 andlegacy terminals because terminals supporting only the features of Rel.8 to 11 (legacy terminals) are capable of using only Legacy DMRS.

It is preferable that switching between Legacy DMRS and Reduced DMRS beflexibly controllable according to the judgment of a base station inconsideration of ensuring uplink scheduling flexibility. As describedabove (see, FIGS. 4B to 4E), providing a plurality of mapping patternsas Reduced DMRS is possible. Accordingly, a DMRS pattern suitable for aterminal needs to be selectable from among a plurality of DMRS patternsincluding a legacy DMRS pattern and a plurality of Reduced DMRS patternsin accordance with the channel quality of terminal, the conditionsaround the terminal, or the data required by the terminal.

It is an object of the present disclosure to provide a terminal, a basestation, a method of generating a DMRS, and a transmission method eachof which allows a DMRS pattern suitable for a terminal to be selectedfrom among a plurality of DMRS patterns including Legacy DMRS andReduced DMRS.

Solution to Problem

A terminal according to an aspect of the present disclosure includes: areception section that receives uplink control information; a controlsection that determines a specific mapping pattern based on the controlinformation from among a plurality of mapping patterns for an uplinkdemodulation reference signal (DMRS); and a generation section thatgenerates a DMRS according to the specific mapping pattern.

A base station according to an aspect of the present disclosureincludes: a control signal generating section that generates uplinkcontrol information based on a mapping pattern to be indicated to aterminal from among a plurality of mapping patterns for an uplinkdemodulation reference signal (DMRS); and a transmission section thattransmits the generated control information.

A method of generating a demodulation reference signal (DMRS) accordingto an aspect of the present disclosure includes: receiving uplinkcontrol information; determining a specific mapping pattern based on thecontrol information from among a plurality of mapping patterns for anuplink DMRS; and generating a DMRS according to the specific mappingpattern.

A transmission method according to an aspect of the present disclosureincludes: generating uplink control information based on a mappingpattern to be indicated to a terminal from among a plurality of mappingpatterns for an uplink demodulation reference signal (DMRS); andtransmitting the generated control information.

Advantageous Effects of Disclosure

According to the present disclosure, a DMRS pattern suitable for aterminal can be selected from among a plurality of DMRS patternsincluding Legacy DMRS and Reduced DMRS.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram illustrating an uplink subframe structure;

FIG. 2 is a block diagram illustrating how sequence groups are assignedfor DMRSs;

FIG. 3 is a diagram illustrating a network configuration in small cellenhancement;

FIGS. 4A, 4B, 4C, 4D, and 4E are diagrams illustrating examples of alegacy DMRS pattern and reduced DMRS patterns;

FIGS. 5A and 5B are diagrams each illustrating orthogonal multiplexingusing a Reduced DMRS pattern by means of OCCs;

FIG. 6 is a diagram illustrating a communication system according toEmbodiment 1 of the present disclosure;

FIG. 7 is a block diagram illustrating a primary configuration of a basestation according to Embodiment 1 of the present disclosure;

FIG. 8 is a block diagram illustrating a configuration of the basestation according to Embodiment 1 of the present disclosure;

FIG. 9 is a block diagram illustrating a primary configuration of aterminal according to Embodiment 1 of the present disclosure;

FIG. 10 is a block diagram illustrating a configuration of the terminalaccording to Embodiment 1 of the present disclosure;

FIG. 11 is a diagram illustrating a correspondence between DPIs and DMRSpatterns according to Embodiment 1 of the present disclosure;

FIG. 12 is a diagram illustrating a correspondence between DPIs, DMRSpatterns, and virtual cell IDs according to Embodiment 1 of the presentdisclosure;

FIG. 13 is a diagram illustrating a correspondence between DPIs, DMRSpatterns, and base sequence group hopping according to Embodiment 1 ofthe present disclosure;

FIG. 14 is a diagram illustrating an example of DMRS pattern indicationaccording to Embodiment 1 of the present disclosure;

FIG. 15 is a diagram illustrating another example of DMRS patternindication according to Embodiment 1 of the present disclosure;

FIG. 16 is a diagram illustrating a relationship between PUSCH bandallocation and each parameter of MV according to Embodiment 2 of thepresent disclosure;

FIG. 17 is a diagram illustrating DMRS patterns corresponding toallocation bandwidths according to Embodiment 2 of the presentdisclosure;

FIG. 18 is a diagram illustrating DMRS patterns corresponding toallocation bandwidths according to Embodiment 2 of the presentdisclosure;

FIG. 19 is a diagram illustrating a correspondence between allocationbandwidths and DMRS patterns according to Embodiment 2 of the presentdisclosure;

FIG. 20 is a diagram illustrating DMRS patterns corresponding toallocation bandwidths according to Embodiment 2 of the presentdisclosure;

FIG. 21 is a diagram illustrating a correspondence between the startpositions of allocation bandwidths and DMRS patterns according toEmbodiment 2 of the present disclosure;

FIG. 22 is a diagram illustrating DMRS patterns corresponding to thestart positions of allocation bandwidths according to Embodiment 2 ofthe present disclosure;

FIGS. 23A and 23B are diagrams each illustrating a correspondencebetween A-SRS trigger bits and DMRS patterns according to Embodiment 3of the present disclosure;

FIG. 24 is a diagram illustrating a correspondence between controlchannels and DMRS patterns according to Embodiment 4 of the presentdisclosure;

FIG. 25 is a diagram illustrating a correspondence between CS fields andDMRS patterns according to Embodiment 5 of the present disclosure;

FIG. 26 is another diagram illustrating a correspondence between CSfields and DMRS patterns according to Embodiment 5 of the presentdisclosure;

FIG. 27 is a diagram illustrating a data mapping sequence according toEmbodiment 6 of the present disclosure; and

FIGS. 28A and 28B are diagrams each illustrating a DMRS pattern in caseof multiplexing with ACK/NACK, according to an additional embodiment ofthe present disclosure.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the drawings. Throughout the embodiments, thesame elements are assigned the same reference numerals and any duplicatedescription of the elements is omitted.

Embodiment 1

(Summary of Communication System)

FIG. 6 illustrates a communication system according to Embodiment 1. Thecommunication system illustrated in FIG. 6 includes base station 100 andone or more terminals 200 within a cell. Referring to FIG. 6, basestation 100 may be a macro cell base station or a small cell basestation. In addition, the communication system may be a HetNet system,which includes a macro cell base station and small cell base stations,or may be a coordinated multipoint (CoMP) system in which a plurality ofbase stations cooperatively communicates with a terminal. Macro cellsand small cells may be operated using different frequencies or the samefrequency.

(Configuration of Base Station 100)

FIG. 7 is a block diagram illustrating primary parts of base station100.

Base station 100 illustrated in FIG. 7 includes control signalgenerating section 11, transmission section 12, reception section 13,channel estimating section 14, and received signal processing section15.

Control signal generating section 11 generates a control signal intendedfor terminal 200 and transmission section 12 transmits the generatedcontrol signal via an antenna. The control signal includes a UL grantindicating PUSCH assignment. A UL grant consists of a plurality of bitsand includes information indicating a frequency allocation resource(resource block (RB)), a modulation and coding scheme, soundingreference signal (SRS) trigger and/or the like. In addition, a UL grantincludes a DMRS pattern indicator (DPI) for specifying a DMRS mappingpattern (DMRS pattern) in transmission of the assigned PUSCH. A DPIconsists of one or more bits. It is assumed that candidate DMRS patternsselectable by DPI are previously indicated to terminal 200 via higherlayers or predetermined. In addition, a control signal is transmittedusing a downlink control channel (physical downlink control channel(PDCCH)) or (enhanced physical downlink control channel (EPDCCH)). AnEPDCCH may be called an EPDCCH set and configured to be mapped within aPDSCH as a new control channel different from a PDCCH.

Specifically, control signal generating section 11 generates an uplinkcontrol information on the basis of a mapping pattern to be indicated toterminal 200 from among a plurality of uplink DMRS mapping patterns.Transmission section 12 transmits the generated control information.

Reception section 13 receives, via an antenna, a PUSCH transmitted fromterminal 200 according to an UL grant and extracts data and a DMRS.Channel estimating section 14 performs channel estimation using theDMRS. Received signal processing section 15 demodulates and decodes thedata on the basis of the estimated channel estimate.

FIG. 8 is a block diagram illustrating base station 100 in detail.

Base station 100 as illustrated in FIG. 8 includes control section 101,control information generating section 102, coding section 103,modulation section 104, mapping section 105, inverse fast Fouriertransform (IFFT) section 106, cyclic prefix (CP) adding section 107,radio transmitting section 108, radio receiving section 109, CP removingsection 110, fast Fourier transform (FFT) section 111, demapping section112, channel state information measuring section 113, channel estimatingsection 114, equalization section 115, inverse discrete Fouriertransform (IDFT) section 116, demodulation section 117, decoding section118, and determination section 119.

Of the components mentioned above, control section 101, controlinformation generating section 102, coding section 103, and modulationsection 104 mainly serve as control signal generating section 11 (see,FIG. 7), and mapping section 105, IFFT section 106, CP adding section107, and radio transmitting section 108 serve as transmission section 12(see, FIG. 7). In addition, radio receiving section 109, CP removingsection 110, FFT section 111, and demapping section 112 mainly serve asreception section 13 (see, FIG. 7), and channel estimating section 114serves as channel estimating section 14, while equalization section 115,IDFT section 116, demodulation section 117, decoding section 118, anddetermination section 119 mainly serve as received signal processingsection 15 (see, FIG. 7).

In base station 100 illustrated in FIG. 8, control section 101determines PUSCH subframe allocation for terminal 200 in accordance withthe conditions of terminal 200 or reception conditions thereof. Controlsection 101 determines the PUSCH subframe allocation for terminal 200 onthe basis of a determination result of received data of terminal 200received as input from determination section 119 (the presence orabsence of an error (ACK or NACK)) and channel state information (CSI)or the like of terminal 200 received as input from CSI measuring section113, for example. Control section 101 determines frequency resourceblock (RB) allocation information, a coding scheme, a modulation scheme,information indicating initial transmission or retransmission, a hybridautomatic repeat request (HARQ) process number, DMRS pattern information(DPI) and/or the like to be indicated to terminal 200, and transmits thedetermined information to control information generating section 102.

Control section 101 determines a coding level for the control signalintended for terminal 200 and outputs the determined coding level tocoding section 103. The coding level is determined in accordance withthe amount of control information included in the control signal to betransmitted or the conditions of terminal 200.

In addition, control section 101 determines a radio resource element(RE) to which the control signal intended for terminal 200 is mapped,and indicates the determined RE to mapping section 105.

Control information generating section 102 generates a controlinformation bit sequence using the control information intended forterminal 200, which is received as input from control section 101, andoutputs the generated control information bit sequence to coding section103. Incidentally, control information may be transmitted to a pluralityof terminals 200. For this reason, control information generatingsection 102 generates the bit sequence while including the terminal IDsof respective terminals 200 in the control information intended forterminals 200. For example, CRC bits masked by the terminal IDs ofdestination terminals 200 are added to the control information.

Coding section 103 encodes the control information bit sequence receivedas input from control information generating section 102, using thecoding level indicated by control section 101. Coding section 103outputs the coded bit sequence to modulation section 104.

Modulation section 104 modulates the coded bit sequence received asinput from coding section 103 and outputs the symbol sequence obtainedby modulation to mapping section 105.

Mapping section 105 maps the control signal received as the symbolsequence from modulation section 104 to the radio resource indicated bycontrol section 101. The control channel to be the mapping target may bea PDCCH or EPDCCH. Mapping section 105 inputs a signal in a downlinksubframe including the PDCCH or EPDCCH to which the control signal ismapped to IFFT section 106.

IFFT section 106 performs an IFFT for the downlink subframe receivedfrom mapping section 105 to transform the frequency-domain signalsequence into a time waveform. IFFT section 106 outputs the timewaveform obtained by transformation to CP adding section 107.

CP adding section 107 adds a CP to the time waveform received as inputfrom IFFT section 106 and outputs the CP-added signal to radiotransmitting section 108.

Radio transmitting section 108 performs transmission processing such asD/A conversion and up-conversion on the signal received as input from CPadding section 107 and transmits the signal resulting from thetransmission processing to terminal 200 via an antenna.

Radio receiving section 109 receives, via an antenna, the uplink signal(PUSCH) transmitted from terminal 200, then performs receptionprocessing such as down-conversion and A/D conversion on the receivedsignal and outputs the signal resulting from the reception processing toCP removing section 110.

CP removing section 110 removes a waveform corresponding to the CP fromthe signal (time waveform) received as input from radio receivingsection 109 and outputs the signal after CP removal to FFT section 111.

FFT section 111 performs an FFT on the signal (time waveform) receivedas input from CP removing section 110 to decompose the signal into afrequency-domain signal sequence (frequency components in units ofsubcarriers) and extracts a signal corresponding to the PUSCH subframe.FFT section 111 outputs the obtained signal to demapping section 112.

Demapping section 112 extracts a PUSCH subframe portion allocated toterminal 200 from the received signal. Demapping section 112 decomposesthe PUSCH subframe extracted from terminal 200 into a DMRS and datasymbols (SC-FDMA data symbols) and outputs the DMRS to channelestimating section 114 and the data symbols to equalization section 115.When terminal 200 transmits a sounding reference signal (SRS) in thePUSCH subframe, demapping section 112 extracts the SRS and outputs theextracted SRS to CSI measuring section 113. When an SRS is transmitted,the last data symbol of the PUSCH subframe is replaced with the SRS.Thus, demapping section 112 may separate the SRS and data symbols inthis case.

Upon receipt of an SRS from demapping section 112, CSI measuring section113 performs CSI measurement using the SRS. CSI measuring section 113then outputs the result of CSI measurement to control section 101.

Channel estimating section 114 performs channel estimation using theDMRS received as input from demapping section 112. Channel estimatingsection 114 outputs the obtained channel estimate to equalizationsection 115.

Equalization section 115 performs equalization of the SC-FDMA datasymbols received as input from demapping section 112, using the channelestimate received as input from channel estimating section 114.Equalization section 115 outputs the equalized SC-FDMA data symbols toIDFT section 116.

IDFT section 116 performs an IDFT of a bandwidth in accordance with theallocation bandwidth on the SC-FDMA data symbols in the frequency-domainto transform the SC-FDMA data symbols into a time-domain signal. IDFTsection 116 outputs the obtained time-domain signal to demodulationsection 117.

Demodulation section 117 performs data demodulation on the time-domainsignal received as input from IDFT section 116. Specifically,demodulation section 117 converts the symbol sequence into a bitsequence on the basis of the modulation scheme indicated to terminal 200and outputs the obtained bit sequence to decoding section 118.

Decoding section 118 performs error correction coding on the bitsequence received as input from demodulation section 117 and outputs thedecoded bit sequence to determination section 119.

Determination section 119 performs error detection on the bit sequencereceived as input from decoding section 118. The error detection isperformed using the CRC bits added to the bit sequence. Determinationsection 119 extracts the received data when the determination on CRCbits results in no error, and indicates ACK to control section 101.Meanwhile, determination section 119 indicates NACK to control section101 when the determination on CRC bits results in an error.

(Configuration of Terminal)

FIG. 9 is a block diagram illustrating a primary configuration of aterminal.

Terminal 200 illustrated in FIG. 9 includes reception section 21,control signal extracting section 22, control section 23, DMRSgenerating section 24, and transmission section 25.

Reception section 21 receives a control signal (UL grant) transmitted toterminal 200 on a PDCCH or EPDCCH and control signal extracting section22 extracts information about allocation of a PUSCH subframe from thecontrol signal. Specifically, control signal extracting section 22blind-decodes allocation candidates of the control signal on apredetermined control channel, and when succeeding in decoding a controlsignal to which CRC bits masked by the terminal ID of terminal 200 areadded, control signal extracting section 22 extracts the control signalas control information intended for terminal 200. The controlinformation includes frequency resource block (RB) allocationinformation, a modulation scheme, information indicating initialtransmission or retransmission, a HARQ process number, A-SRS trigger(aperiodic SRS transmission request), DMRS pattern information (DPI)and/or the like.

Control section 23 determines a PUSCH subframe structure on the basis ofthe extracted control information (UL grant). Control section 23determines the DMRS pattern to be used according to the value of DPIincluded in the UL grant, for example. DMRS generating section 24generates a DMRS according to the indication from control section 23.Transmission section 25 transmits a PUSCH subframe signal including theDMRS according to the indication from control section 23.

More specifically, reception section 21 receives uplink controlinformation, and control section 23 determines a specific mappingpattern from among a plurality of mapping patterns for uplink DMRSs onthe basis of the control information. DMRS generating section 24generates a DMRS according to the specific mapping pattern.

FIG. 10 is a block diagram illustrating terminal 200 in detail.

Terminal 200 illustrated in FIG. 10 includes radio receiving section201, CP removing section 202, FFT section 203, control signal extractingsection 204, control section 205, coding section 206, modulation section207, DMRS generating section 208, SRS generating section 209,multiplexing section 210, discrete Fourier transform (DFT) section 211,mapping section 212, IFFT section 213, CP adding section 214, and radiotransmitting section 215.

Of the components mentioned above, radio receiving section 201, CPremoving section 202, and FFT section 203 mainly serve as receptionsection 21 (see, FIG. 9). In addition, coding section 206, modulationsection 207, SRS generating section 209, multiplexing section 210, DFTsection 211, mapping section 212, IFFT section 213, CP adding section214, and radio transmitting section 215 mainly serve as transmissionsection 25 (see, FIG. 9). Moreover, control signal extracting section204 serves as control signal extracting section 22, and control section205 serves as control section 23. DMRS generating section 208 serves asDMRS generating section 24.

In terminal 200 illustrated in FIG. 10, radio receiving section 201receives, via an antenna, a control signal (PDCCH or EPDCCH) transmittedfrom base station 100 (see, FIG. 8), then perform reception processingsuch as down-conversion and A/D conversion on the control signal andoutputs the control signal subjected to the reception processing to CPremoving section 202.

CP removing section 202 removes a CP from a downlink subframe signalincluding a PDCCH or EPDCCH from the control signal received as inputfrom radio receiving section 201 and outputs the signal after CP removalto FFT section 203.

FFT section 203 performs an FFT on the signal (downlink subframe)received as input from CP removing section 202, to transform the signalinto a frequency-domain signal. FFT section 203 outputs thefrequency-domain signal to control signal extracting section 204.

Control signal extracting section 204 performs blind-decoding on thefrequency-domain signal received as input from FFT section 203 toattempt decoding of the control signal. The control signal intended forterminal 200 includes a CRC masked by the terminal ID of terminal 200and added to the control signal. Accordingly, when a CRC judgment on theresult of blind-decoding in OK, control signal extracting section 204extracts and outputs the control signal to control section 205.

Control section 205 controls PUSCH transmission on the basis of thecontrol signal received as input from control signal extracting section204.

Specifically, control section 205 indicates RB allocation for PUSCHtransmission to mapping section 212 on the basis of the PUSCH RBallocation information included in the control signal. Moreover, controlsection 205 indicates a coding method and a modulation scheme for PUSCHtransmission to coding section 206 and modulation section 207 on thebasis of the information on the coding method and modulation scheme,respectively. Control section 205 also indicates, on the basis of an SRStrigger included in the control information, whether or not to transmitan SRS after a certain period of time passes. The SRS indicated by theSRS trigger may be transmitted while being multiplexed in the PUSCHsubframe indicated by the UL grant, or may be transmitted in a subframetransmitted after the PUSCH subframe. In addition, control section 205determines the DMRS pattern for PUSCH transmission on the basis of theDPI included in the control signal and indicates the determined DMRSpattern to DMRS generating section 208.

Coding section 206 performs error correction coding by adding CRC bitsmasked by the terminal ID to the transmission data received as input.The coding rate, codeword length and/or the like for coding section 206to perform the error correction coding are indicated by control section205. Coding section 206 outputs a coded bit sequence to modulationsection 207.

Modulation section 207 modulates the bit sequence received as input fromcoding section 206. The modulation level (i.e., m-ary modulation number)and the like for modulation section 207 to perform the modulation areindicated by control section 205. Modulation section 207 outputs themodulated data symbol sequence to multiplexing section 210.

DMRS generating section 208 generates a DMRS according to the DMRSpattern indicated by control section 205 and outputs the DMRS tomultiplexing section 210.

SRS generating section 209 generates an SRS according to an indicationfrom control section 205 and outputs the SRS to multiplexing section210. It should be noted herein that, the transmission timing of SRS isnot necessarily the same as that of the PUSCH subframe indicated by theUL grant.

Multiplexing section 210 multiplexes the data symbol sequence, DMRS, andSRS respectively received as input from modulation section 207, DMRSgenerating section 208, and SRS generating section 209, then multiplexesthe data symbol sequence, DMRS, and SRS, and outputs the multiplexedsignal to DFT section 211.

DFT section 211 performs a DFT on the signal received as input frommultiplexing section 210, then decomposes the signal into frequencycomponent signals in units of subcarriers, and outputs the obtainedfrequency component signals to mapping section 212.

Mapping section 212 maps the signals received as input from DFT section211 (i.e., data symbol sequence, DMRS, and SRS), according to theindication from control section 205 to time and frequency resourcesallocated in the PUSCH subframe. Mapping section 212 outputs the PUSCHsubframe signal to IFFT section 213.

IFFT section 213 performs an IFFT on the PUSCH subframe signal in thefrequency-domain, which is received as input from mapping section 212,to transform the frequency-domain signal into a time-domain signal. IFFTsection 213 outputs the time-domain signal obtained by thetransformation to CP adding section 214.

CP adding section 214 adds a CP to the time-domain signal received asinput from IFFT section 213 (every output from IFFT section 213) andoutputs the CP-added signal to radio transmitting section 215.

Radio transmitting section 215 performs transmission processing such asD/A conversion and up-conversion on the signal received as input from CPadding section 214 and transmits the signal subjected to thetransmission processing to base station 100 via an antenna.

(Operation)

A processing flow of base station 100 and terminal 200 according toEmbodiment 1 will be described using steps (1) to (4).

Step (1): Prior to transmission and reception of a PUSCH, base station100 indicates to terminal 200 that a plurality of DMRS patterns may bespecified. DMRS patterns that may be specified can be predetermined orindicated to terminal 200 by base station 100 from a plurality ofcandidates via higher layers. The DMRS patterns that may be specifiedincludes reduced DMRS patterns as illustrated in FIGS. 4B to 4E andFIGS. 5A and 5B in addition to the legacy DMRS pattern (see, e.g., FIG.4A) used in Rel. 8 to 10, for example.

In step (1), the indication to terminal 200 may be made by base station100 that performs the transmission and reception of PUSCH, or may bemade by base station 100 other than base station 100 that performs thetransmission and reception of PUSCH. For example, base station 100 thatperforms the transmission and reception of PUSCH may be a small cellbase station and a base station that makes the indication may be a macrocell base station in step (1).

Step (2): Base station 100 transmits a control signal (UL grant) toterminal 200 via a PDCCH or EPDCCH to indicate PUSCH assignment. The ULgrant includes a DMRS pattern indicator (DPI) indicating a DMRS pattern.The DPI indicates one specific DMRS pattern from a plurality ofcandidate DMRS patterns to terminal 200. Specifically, base station 100(control section 101) generates the DPI on the basis of the specificDMRS pattern to be indicated to terminal 200.

FIG. 11 illustrates an example when a DPI consists of two bits. In FIG.11, the legacy DMRS pattern and reduced DMRS patterns (1) to (3) areassociated respectively with the values of DPI.

It should be noted herein that, the UL grant including a DPI may betransmitted to terminal 200 from base station 100 that performs thetransmission and reception of PUSCH or from base station 100 other thanthe base station that performs the transmission and reception of PUSCH.For example, base station 100 that performs the transmission andreception of PUSCH may be a small cell base station, and the basestation that performs the transmission of UL grant may be a macro cellbase station.

Step (3): Terminal 200 blind-decodes a PDCCH or EPDCCH received in step(2) and acquires the control signal (UL grant) intended for theterminal. When the UL grant includes a DPI, terminal 200 (controlsection 205) determines a specific DMRS pattern to be used by terminal200 from a plurality of candidate DMRS patterns on the basis of the DPI.Terminal 200 (DMRS generating section 208) generates a DMRS used for thePUSCH transmission according to the specific DMRS pattern.

Step (4): Base station 100 receives the PUSCH transmitted from terminal200 in step (3) and performs channel estimation on the basis of the DMRSextracted from the PUSCH subframe. Base station 100 performsequalization, demodulation, and decoding of the data symbols using theobtained channel estimate.

When determining that the data is correctly decoded, base station 100transmits ACK to terminal 200 to prompt the next data transmission. Whendetermining that the decoding result of data includes an error, basestation 100 transmits NACK to terminal 200 to prompt HARQretransmission.

(Advantageous Effects)

As described above, base station 100 indicates any one of thepredetermined plurality of DMRS patterns to terminal 200, using the DPIincluded in the UL grant on the downlink control channel (PDCCH orEPDCCH). Terminal 200 identifies the DMRS pattern in the PUSCH subframeaccording to the DPI included in the UL grant transmitted from basestation 100.

According to the processing flow, base station 100 can dynamicallyswitch between DMRS patterns for terminal 200. According to Embodiment1, a DMRS pattern suitable for terminal 200 can be selected from among aplurality of DMRS patterns including a legacy DMRS pattern and reducedDMRS patterns.

Base station 100 can dynamically switch between a DMRS pattern thatallows reception with high channel estimation accuracy (legacy DMRSpattern) and a DMRS pattern involving low overhead (reduced DMRSpattern) in accordance with the conditions or environment of terminal200, for example. Thus, according to Embodiment 1, higher reliabilityand an increase in communication volume can be flexibly achieved.

In addition, when a legacy terminal (e.g., terminal supporting thefeatures of Rel. 10) exists in the cell, for example, base station 100may perform spatial multiplexing for the legacy terminal and terminal200 by means of CS and OCCs by instructing terminal 200 to use LegacyDMRS. Moreover, base station 100 may cause terminal 200 to transmit datausing a low overhead PUSCH subframe by indicating terminal 200 to use areduced DMRS pattern. In this manner, base station 100 can flexiblyindicate uplink scheduling for terminal 200. Thus, according toEmbodiment 1, characteristic degradation due to the schedulingrestrictions can be avoided.

Particularly, since the number of terminals performing communicationsimultaneously is small in a small cell, it is expected that there isnot much traffic on the downlink control channel. Moreover, the distancebetween a small cell base station and each terminal is relatively shortin a small cell, so that a possible decrease in the coverage associatedwith addition of bits for DPI in the control channel does not matter.Stated differently, according to Embodiment 1, indicating a DMRS patternusing a DPI makes it possible to flexibly switch between DMRS patternswithout any significant drawback.

(Variation 1)

In variation 1, a DPI indicates a DMRS pattern, and a virtual cell ID(VCID) or cell ID (PCID).

Specifically, base station 100 previously indicates, to terminal 200,not only a DMRS pattern that may be specified, but also a virtual cellID corresponding to the value of each DPI. Base station 100 indicatesuse of a certain DMRS pattern and the virtual cell ID (or cell ID)corresponding to the DMRS pattern by use of the DPI. Terminal 200identifies the DMRS pattern and virtual cell ID (or cell ID) on thebasis of the DPI and generates a DMRS.

FIG. 12 illustrates a correspondence between the values of DPI, DMRSpatterns and virtual cell IDs. When DPI is “00,” terminal 200 generatesa DMRS using a base sequence corresponding to the legacy DMRS patternand cell ID with reference to FIG. 12. In addition, when DPI is “10,”terminal 200 generates a DMRS using a base sequence corresponding to thereduced DMRS pattern (pattern 2) and virtual cell ID 1 (VCID 1) withreference to FIG. 12. Terminal 200 generates a DMRS in the same mannerwhen DPI is “01” and “11.”

As described above, Reduced DMRS is often used when the channel state ofterminal 200 is good (e.g., when the distance between terminal 200 andbase station 100 is relatively short). Such a good channel state islikely to occur when terminal 200 is connected to a small cell basestation. Meanwhile, it is possible that small cell base stations may bedeployed unevenly: for example, a large number of small cell basestations are deployed densely; or small cell base stations are deployedsparsely and not densely.

Accordingly, interference control between small cells using virtual cellIDs may be flexibly performed using orthogonalization of interference byindicating the same virtual ID or randomization of interference byindicating different virtual cell IDs to a plurality of small cell basestations. Stated differently, Reduced DMRS and virtual cell IDs arelikely to be used simultaneously.

In this respect, as illustrated in FIG. 12, indicating a DMRS patternand virtual cell ID simultaneously to terminal 200 by base station 100using a DPI makes it possible to instruct terminal 200 to use bothReduced DMRS and a virtual cell ID by the DPI alone. Thus, interferencecontrol between small cells can be more flexibly and appropriatelyperformed while an increase in overhead is minimized.

(Variation 2)

In variation 2, a DPI indicates a DMRS pattern and ON/OFF of a basesequence group hopping.

Base sequence group hopping is a method introduced in Rel. 8 and usedfor reducing more intercell interference by means of hopping between thegroup numbers of base sequence groups so as to generate a DMRS using adifferent base sequence group for each DMRS transmission. Meanwhile,when base sequence group hopping is performed, different base sequencesare used for two DMRSs in a PUSCH subframe, which raises a problem inthat multiplexing between terminals by means of OCCs cannot beperformed. For this reason, the feature to quasi-statically turn ON/OFFthe base sequence group hopping by higher layer signaling is added inRel. 10, thus making possible achieving multiplexing by means of OCCs.

Base station 100 previously indicates not only DMRS patterns that may bespecified and but also ON/OFF of base sequence group hoppingcorresponding to each value of DPI to terminal 200. Base station 100indicates a DMRS pattern and the ON/OFF of base sequence group hoppingcorresponding to the DMRS pattern, using the DPI. Terminal 200identifies the DMRS pattern and the ON/OFF of base sequence grouphopping corresponding to the DMRS pattern on the basis of the DPI.

FIG. 13 illustrates a relationship between DPI values, DMRS patterns,and ON/OFF of base sequence group hopping. For example, referring toFIG. 13, when DPI is “00,” terminal 200 generates a DMRS using LegacyDMRS and turning ON the base sequence group hopping. In addition, whenDPI is “11,” terminal 200 generates a DMRS using Reduced DMRS (Pattern2) and turning OFF the base sequence group hopping. Terminal 200generates a DMRS in the same manner when DPI is “01” and “10.”

FIG. 14 illustrates an example of a case where a DMRS pattern and ON/OFFof the base sequence group hopping are indicated using the DPIillustrated in FIG. 13. FIG. 14 illustrates four subframes, eachconsisting of two slots.

As illustrated in FIG. 14, since DPI is equal to “00” in the first andfourth subframes, terminal 200 uses Legacy DMRS and performs hoppingbetween base sequence groups of two DMRSs in each of the subframes(sequence group numbers: #3 and #15, and #26 and #5). Accordingly,randomization of interference to a different cell is made possible.

In addition, as illustrated in FIG. 14, since DPI is equal to “01” inthe second subframe, terminal 200 generates DMRSs using Legacy DMRS anda sequence determined by the cell ID or virtual cell ID (sequence groupnumber: #3 in this example) without hopping between base sequencegroups. Accordingly, orthogonalization of interference by means of OCCsis made possible.

As illustrated in FIG. 14, since DPI is equal to “11” in the thirdsubframe, terminal 200 generates DMRSs using Reduced DMRS withouthopping between base sequence groups. Accordingly, overhead reduction byReduced DMRS is made possible.

Turning ON the base sequence group hopping allows for randomization ofinterference, but makes orthogonalization of interference by means ofOCCs no longer possible. On the other hand, turning OFF the basesequence group hopping allows for orthogonalization by means of OCCs,but does not randomize interference. For this reason, base station 100indicates a DMRS pattern and ON/OFF of the base sequence group hoppingusing a DPI at once. Accordingly, terminal 200 can dynamically switchbetween DMRS patterns and also between ON and OFF of the base sequencegroup hopping in accordance with the conditions of terminal 200,interference to an adjacent cell, or the presence or absence of aterminal subject to spatial multiplexing. Thus, according to variation2, it is possible to flexibly minimize interference and increase thethroughput.

(Variation 3)

In variation 2 (see, FIG. 14), the sequence determined by the cell ID orvirtual cell ID is used in all the slots when base sequence grouphopping is OFF (sequence group #3 in FIG. 14). On the other hand, invariation 3, when base sequence group hopping is OFF in a certainsubframe, terminal 200 uses a DMRS sequence group to be used in thefirst slot of the same subframe when the base sequence group hopping isON, in the two slots of the certain subframe.

FIG. 15 illustrates an example of a case where a DMRS pattern and theON/OFF of base sequence group hopping are indicated using the DPIillustrated in FIG. 13. In FIG. 15, four subframes are illustrated, asin the case of FIG. 14, and each subframe consists of two slots.

As illustrated in FIG. 15, since DPI is equal to “01” in the secondsubframe, no hopping is performed between base sequence groups.Meanwhile, the sequence group number of the DMRS used in the first slotof the second subframe when hopping between base sequence groups isperformed is #6. Thus, terminal 200 generates DMRSs using Legacy DMRSand the sequence group #6 without hopping between the base sequencegroups in the second subframe.

Likewise, as illustrated in FIG. 15, since DPI is equal to “11” in thethird subframe, no hopping is performed between base sequence groups.Meanwhile, the sequence group number of the DMRS used in the first slotof the third subframe when hopping between base sequence groups isperformed is #7. Thus, terminal 200 generates DMRSs using Reduced DMRSand the sequence group #7 without hopping between base sequence groupsin the third subframe.

Specifically, while the DMRS of sequence group number #3 is always usedwhen hopping between sequence groups is OFF in variation 2 (see, FIG.14), the sequence group number is changed even when hopping betweensequence groups is OFF (the second and third subframes) in variation 3(see, FIG. 15).

Accordingly, switching between the DMRS sequence groups to be used isperformed at least every 1 ms (one subframe) for any terminal 200. Thus,in addition to the effects obtained in variation 2, the effect ofrandomization of interference to an adjacent cell is obtained.

Embodiment 2

(Summary of Communication System)

A communication system according to Embodiment 2 includes base station100 and one or more terminals 200 as in Embodiment 1 (see, FIG. 6).

In Embodiment 2, unlike Embodiment 1, however, the DPI indicating a DMRSpattern is not used, but RB allocation information and a DMRS patternare indicated simultaneously by the value of resource indication value(MV) included in a UL grant. Specifically, a plurality of DMRS patternsare associated with the values of MV, which is the existing RBallocation information on uplink included in the control informationtransmitted from base station 100 to terminal 200. Stated differently,DMRS patterns are indicated using the existing RIV.

Specifically, a plurality of DMRS patterns that may be specified arepreviously indicated to terminal 200, and also DMRS patternscorresponding to the values of RIV are previously indicated to terminal200. Terminal 200 identifies an RB used for the transmission of PUSCHsubframe, on the basis of the value of RIV indicated by base station 100and determines the DMRS pattern corresponding to the MV as the DMRSpattern used in the transmission of PUSCH subframe. Incidentally, theplurality of DMRS patterns that may be specified, and the DMRS patternscorresponding to the values of RIV may be previously indicated toterminal 200 by base station 100 via higher layers, or onlypredetermined combinations may be used.

(Configuration of Base Station 100)

Control section 101 of base station 100 determines a PUSCH subframeassignment to terminal 200. Control section 101 herein determines thevalue of RB allocation information (MV) in consideration of both of anRB to be allocated to terminal 200 and a DMRS pattern to be indicated toterminal 200.

(Configuration of Terminal 200)

Control section 205 of terminal 200 indicates RB allocation for thePUSCH transmission to mapping section 212 on the basis of the value ofRIV included in the UL grant. Moreover, control section 205 determinesthe DMRS pattern for the PUSCH transmission on the basis of the value ofRIV.

(Operation)

A description will be provided regarding operation of base station 100and terminal 200 according to Embodiment 2. The processing flow of basestation 100 and terminal 200 according to Embodiment 2 is substantiallythe same as steps (1) to (4).

However, unlike Embodiment 1, the UL grant includes no DPI in Embodiment2. Instead, base station 100 configures the value of RIV on the basis ofthe DMRS pattern to be indicated to terminal 200, and terminal 200determines the DMRS pattern used in the PUSCH subframe on the basis ofthe value of RIV included in the UL grant.

An MV is information indicated by the number of bits in accordance withthe system bandwidth (e.g., when no frequency hopping for PUSCH isperformed, Log₂(N_(RB) ^(UL)(N_(RB) ^(UL)+1)/2) bits), and the value ofMV is determined on the basis of equation 1 below (when no frequencyhopping for PUSCH is performed).

[1]                                                                               (Equation  1)$\left\{ \begin{matrix}\begin{matrix}{{RIV} = {{N_{RB}^{UL}\left( {L_{CRBs} - 1} \right)} +}} \\{{RB}_{START},}\end{matrix} & {{{if}\mspace{14mu} \left( {L_{CRBs} - 1} \right)} \leq \left\lfloor {N_{RB}^{UL}/2} \right\rfloor} \\\begin{matrix}{{RIV} = {{N_{RB}^{UL}\left( {N_{RB}^{UL} - \left( {L_{CRBs} - 1} \right)} \right)} +}} \\{\left( {N_{RB}^{UL} - 1} \right) - {RB}_{START}}\end{matrix} & {else}\end{matrix} \right.$

In equation 1, N_(RB) ^(UL) represents the uplink system bandwidth andL_(CRBs) represents the number of allocation RBs to terminal 200, whileRB_(START) represents the RB corresponding to the lowest frequency ofthe allocation RBs of terminal 200. In addition, equation 1 is used forcontiguous band allocation. The value of MV indicated in equation 1uniquely defines the number of RBs allocated to terminal 200 and thepositions of the RBs (see, FIG. 16). There is a restriction that onlymultiple numbers of 2, 3, and 5 are selectable for L_(CRBs). For thisreason, in the structure of Rel. 11 or before, any value of MVcorresponding to L_(CRBs) other than multiple numbers of 2, 3, and 5 isnot indicated.

(Advantageous Effects)

As described above, base station 100 indicates any one of a plurality ofDMRS patterns to terminal 200 using the frequency resource allocationinformation (MV) indicating the frequency resource allocationinformation bits included in a UL grant. Terminal 200 identifies theDMRS pattern to be used from the plurality of DMRS patterns on the basisof the value of MV included in the received UL grant.

As described above, when Reduced DMRS is indicated to terminal 200, itis likely that terminal 200 communicates with a small cell base station.In addition, the number of terminals simultaneously performingcommunication is likely to be small in a small cell, and the channelquality of terminals communicating with the small cell is likely to begood. For this reason, even if the scheduling granularity in thefrequency-domain is reduced, the frequency-domain scheduling gain cannotbe increased in small cells. In other words, when the schedulinggranularity is reduced to identifying more DMRS patterns, there isalmost no influence of the drawback. Accordingly, identifying the DMRSpattern used in terminal 200 in accordance with the value of MV enablesflexible switching between DMRS patterns.

Moreover, in Embodiment 2, the existing RIV is used to indicate DMRSpatterns. Accordingly, since no additional bits for indicating DMRSpatterns are required, there is no increase in overhead.

Next, a description will be provided in detail regarding specificexamples 1 to 4 of indicating and identifying DMRS patterns in basestation 100 and terminal 200 in Embodiment 2.

(Specific Example 1)

Base station 100 configures the value of the number of allocation RBs(i.e., allocation bandwidth) L_(CRBs) in RIV, to be either even or oddin consideration of DMRS patterns. Terminal 200 identifies the DMRSpattern to be used, according to whether the value of the number ofallocation RBs (i.e., allocation bandwidth) L_(CRBs) in RIV included ina UL grant is even or odd.

For example, the RIV indicating an odd number of allocation RBs isassociated with a legacy DMRS pattern, and the RIV indicating an oddnumber of RBs is associated with a Reduced DMRS pattern. Specifically,terminal 200 uses Legacy DMRS when an RIV including L_(CRBs) equivalentto an odd number of RBs is indicated by base station 100, while usingReduced DMRS when an MV including L_(CRBs) equivalent to an even numberof RBs is indicated by base station 100.

It should be noted that, the associations between the numbers ofallocation RBs represented by L_(CRBs) (even or odd RBs) and whether ornot to use Reduced DMRS are previously determined or shared between basestation 100 and terminal 200 via higher layer signaling or the like. Inaddition, the reduced DMRS patterns specified by MV may be previouslydetermined, or may be indicated to terminal 200 by base station 100using higher layers or the like.

FIG. 17 illustrates an example of DMRS pattern indication in specificexample 1. In FIG. 17, reduced DMRS pattern (3) illustrated in FIG. 4Dis used as an example in the case of Reduced DMRS.

As illustrated in FIG. 17, when L_(CRBs) in the RIV indicated by the ULgrant is odd (1 RB or 3 RBs), the legacy DMRS pattern is used as theDMRS pattern. Meanwhile, when L_(CRBs) in the MV indicated by the ULgrant is even (2 RBs or 4 RBs), reduced DMRS pattern (3) is used as theDMRS pattern.

Although only one kind of reduced DMRS pattern is associated with thecase where L_(CRBs) is even RBs, different patterns of a plurality ofreduced DMRS patterns may be associated respectively with differentvalues of L_(CRBs) (e.g., 2 RBs and 4 RBs).

Incidentally, a sequence length corresponding to L_(CRBs) of an integeris defined for the existing DMRS. Accordingly, when L_(CRBs) is odd, aDMRS of a sequence length corresponding to half of L_(CRBs) exists.Meanwhile, when L_(CRBs) is even, a sequence length obtained by dividingL_(CRBs) by power of two (e.g., two) cannot be defined.

For this reason, when L_(CRBs) is even, terminal 200 can use theexisting DMRS of a sequence length corresponding to half of L_(CRBs)even when using a reduced DMRS pattern. More specifically, when it isdefined that Reduced DMRS is used only when L_(CRBs) is even, and LegacyDMRS is used when L_(CRBs) is odd as illustrated in FIG. 17, terminal200 can generate a DMRS of a bandwidth equal to half of a PUSCH can begenerated only using a DMRS of the existing sequence length. Stateddifferently, it is unnecessary to define a DMRS of a new sequence lengthother than the existing sequence lengths for use in Reduced DMRS.

In addition, it is expected that Reduced DMRS is likely to be used insmall cells, that the frequency selectively for channel quality is low,and that the number of terminals communicating simultaneously is small.In other words, Reduced DMRS is likely to be used in an environmentwhere there is no drawback of coarse scheduling granularity in thefrequency-domain. For this reason, associating the number of allocationRBs (allocation bandwidth) in RIV with a DMRS pattern imposesrestrictions on flexibility of RIV, but involves almost no influence ofthe drawback due to the restrictions, and enables dynamically indicatingReduced DMRS.

(Variation of Specific Example 1)

In this variation, the RIV indicating an odd number of allocation RBs isassociated with this odd number plus one allocation RBs and a reducedDMRS pattern, and the RIV indicating an even number of allocation RBs isassociated with the legacy DMRS pattern.

Specifically, when an MV including L_(CRBs) equivalent to an odd numberof RBs is indicated to terminal 200, terminal 200 uses Reduced DMRSassuming that the number of RBs is (L_(CRBs)+1), and when an MVincluding L_(CRBs) equivalent to an even number of RBs is indicated toterminal 200, terminal 200 uses Legacy DMRS assuming that the number ofRBs is L_(CRBs).

It should be noted that, the associations between the numbers ofallocation RBs represented by L_(CRBs) (odd or even RBs) and whether ornot to use Reduced DMRS are previously determined or shared between basestation 100 and terminal 200 via higher layer signaling or the like. Inaddition, the reduced DMRS patterns specified by RIV may be previouslydetermined, or may be indicated to terminal 200 by base station 100using higher layers or the like.

FIG. 18 illustrates an example of DMRS pattern indication in thevariation of specific example 1. As in FIG. 17, reduced DMRS pattern (3)illustrated in FIG. 4D is used as an example in the case of ReducedDMRS.

As illustrated in FIG. 18, when L_(CRBs) in the MV indicated by the ULgrant is even (2 RBs or 4 RBs), the allocation bandwidth is configuredaccording to L_(CRBs), and the legacy DMRS pattern is used as the DMRSpattern. Meanwhile, as illustrated in FIG. 18, when L_(CRBs) in the RIVindicated by the UL grant is odd (1 RB or 3 RBs), the allocationbandwidth is configured according to L_(CRBs) plus one (i.e., 2 RBs or 4RBs), and reduced DMRS pattern (3) is used as the DMRS pattern.

According to this variation, unlike specific example 1 (see, FIG. 17),there are allocation bandwidths (odd number of allocation RBs) thatcannot be specified for terminal 200 to which Reduced DMRS can beindicated, but Legacy DMRS and Reduced DMRS become selectable in thesame allocation bandwidths (even number of allocation RBs). Morespecifically, since terminal 200 can select one DMRS pattern from amonga plurality of DMRS patterns including Legacy DMRS and Reduced DMRS inthe same allocation bandwidths, there is no need to change a bandwidthfor selecting a DMRS pattern. Accordingly, the circuit configuration andalgorithm of scheduler can be more simplified.

Incidentally, when an RIV including L_(CRBs) equivalent to an evennumber of RBs is indicated to terminal 200, terminal 200 may use LegacyDMRS assuming that the number of RBs is (L_(CRBs)+1), and when an MVincluding L_(CRBs) equivalent to an even number of RBs is indicated toterminal 200, terminal 200 may use Reduced DMRS assuming that the numberof RBs is L_(CRBs).

In addition, an MV indicating an odd number of allocation RBs isassociated with this odd number minus one allocation RBs, and a reducedDMRS pattern.

(Specific Example 2)

Base station 100 configures the value of the number of allocation RBs(allocation bandwidth) L_(CRBs) in MV in consideration of the DMRSpattern. Terminal 200 identifies the DMRS pattern to be used, incomparison between the value of the number of allocation RBs (allocationbandwidth) L_(CRBs) in MV included in a UL grant and a predeterminedvalue.

For example, the RIV indicating an allocation bandwidth not greater thanpredetermined value x is associated with the legacy DMRS pattern, andthe RIV indicating an allocation bandwidth greater than predeterminedvalue x is associated with a reduced DMRS pattern. Specifically,terminal 200 uses Legacy DMRS when L_(CRBs) satisfies 0<L_(CRBs)≤x, anduses Reduced DMRS when L_(CRBs) satisfies x<L_(CRBs)≤N_(RB) ^(UL) in theRIV indicated by base station 100.

In other words, the DMRS pattern used by terminal 200 is switched foreach range of the bandwidth allocated to terminal 200.

It is assumed that whether or not to use Reduced DMRS when L_(CRBs)satisfies x<L_(CRBs)≤N_(RB) ^(UL) is previously determined or is sharedbetween base station 100 and terminal 200 via higher layer signaling orthe like. Moreover, the reduced DMRS patterns specified by L_(CRBs) maybe previously determined, or may be indicated to terminal 200 by basestation 100 using higher layers or the like.

In addition, it is assumed that predetermined value x (0<x<N_(RB) ^(UL))is previously determined or is shared between base terminal 100 andterminal 200 via higher layer signaling or the like.

Moreover, a plurality of values (x₁, x₂ . . . ) may be indicated as x,and the DMRS pattern used by terminal 200 may be switched among aplurality of DMRS patterns in accordance with the value of L_(CRBs).

FIGS. 19 and 20 illustrate an example of DMRS pattern indication when aplurality of predetermined values x₁, x₂, and x₃ are used.

In FIG. 19, the following values are configured: x₁=2, x₂=8, and x₃=15,while N_(RB) ^(UL)=25. With this configuration, when L_(CRBs) satisfies0<L_(CRBs)≤x₁, (i.e., L_(CRBs)=1 to 2), legacy DMRS is used; whenL_(CRBs) satisfies x₁<L_(CRBs)≤x₂, (i.e., L_(CRBs)=3 to 8), reduced DMRSpattern (1) is used; when L_(CRBs) satisfies x₂<L_(CRBs)≤x₃, (i.e.,L_(CRBs)=9 to 15), reduced DMRS pattern (2) is used; and when L_(CRBs)satisfies x₃<L_(CRBs)≤N_(RB) ^(UL), (i.e., L_(CRBs)=16 to 25), reducedDMRS pattern (3) is used. As illustrated in FIG. 20, reduced DMRSpattern (1) illustrated in FIG. 19 corresponds to reduced DMRS pattern(1) illustrated in FIG. 4B. Reduced DMRS patterns (2) and (3) are each amethod in which one of two DMRSs included in the legacy DMRS pattern(FIG. 4A) is replaced with data, and DMRSs each having a sequence lengthshorter than the allocation bandwidth are mapped to the remaining DMRSfrequency resource in a distributed manner in the SC-FDMA symbol.

As described above, in specific example 2, Legacy DMRS is selected whenthe RIV specifies a bandwidth for the number of RBs not greater than apredetermined value (x in FIGS. 19 and 20), and one DMRS pattern isselected from among one or more reduced DMRS patterns when the MVspecifies a bandwidth for the number of RBs greater than thepredetermined value.

Terminal 200 capable of Reduced DMRS is typically one which is connectedto a small cell or which has good channel quality. In this case, thebandwidth to be allocated to terminal 200 is likely to be wide. In otherwords, the better the channel quality of terminal 200 is, the morelikely that terminal 200 is allocated a wide band. Moreover, when thechannel quality of terminal 200 is good, it is possible to performchannel estimation with sufficient accuracy using less energy or lessDMRS resources.

Accordingly, as in specific example 2, the DMRS pattern is changed foreach allocation bandwidth of terminal 200, and the DMRS energy orresources are reduced when a wider band is allocated. Thus, theresources that have become available by reducing the DMRS resources canbe allocated to data. Specifically, as illustrated in FIGS. 19 and 20,the wider the allocation bandwidth is, the lower the density of DMRS ina subframe will be.

As described above, indicating a wider allocation bandwidth and ReducedDMRS to terminal 200 which has good channel quality and which requires ahigh data rate, to thereby provide more data resources makes it possibleto achieve higher throughput. Meanwhile, indicating a narrow allocationbandwidth and Legacy DMRS to terminal 200 for which high channelestimation accuracy is required, or terminal 200 for which MU-MIMO witha legacy terminal is required makes it possible to improve the channelestimation accuracy or application of MU-MIMO.

(Specific Example 3)

Base station 100 configures the value of lowest RB position RB_(START)of the allocation bandwidth in the RIV in consideration of the DMRSpattern. Terminal 200 specifies the DMRS pattern to be used, incomparison between the value of RB position RB_(START) and apredetermined value in the RIV included in the UL grant.

For example, the RIV in which the lowest frequency of allocation band ishigher than predetermined value y is associated with the legacy DMRSpattern, and the RIV in which the lowest frequency of allocation band isnot higher than predetermined value y is associated with a reduced DMRSpattern. Specifically, terminal 200 uses Reduced DMRS when RB_(START)satisfies 0≤RB_(START)≤y in the RIV indicated by base station 100, andterminal 200 uses Legacy DMRS when RB_(START) satisfiesy<RB_(START)<N_(RB) ^(UL) in the RIV indicated by base station 100.

In other words, the DMRS pattern used by terminal 200 is switched foreach start position of the band allocated to terminal 200.

It is assumed that whether or not to use Reduced DMRS when RB_(START)satisfies 0≤RB_(START)≤y is previously determined or is shared betweenbase station 100 and terminal 200 via higher layer signaling or thelike. Moreover, the reduced DMRS patterns specified by RB_(START) may bepreviously determined, or may be indicated to terminal 200 by basestation 100 using higher layers or the like.

In addition, it is assumed that predetermined value y (0≤y<N_(RB) ^(UL))is previously determined or is shared between base terminal 100 andterminal 200 via higher layer signaling or the like.

Moreover, a plurality of values (y₁, y₂ . . . ) may be indicated as y,and the DMRS pattern used by terminal 200 may be switched among aplurality of DMRS patterns in accordance with the value of RB_(START).

FIGS. 21 and 22 illustrate an example of DMRS pattern indication when aplurality of predetermined values y₁, y, and y₃ are used.

In FIG. 21, the following values are configured: y₁=10, y₂=15, andy₃=20, while N_(RB) ^(UL)=25. With this configuration, when RB_(START)satisfies 0<RB_(START)≤y₁, (i.e., RB_(START)=0 to 10), reduced DMRSpattern (3) is used; when RB_(START) satisfies y₁<RB_(START)≤y₂, (i.e.,RB_(START)=11 to 15), reduced DMRS pattern (2) is used; when RB_(START)Satisfies y₂<RB_(START)≤y₃, (i.e., RB_(START)=16 to 20), reduced DMRSpattern (1) is used; and when RB_(START) satisfies y₃<RB_(START)≤N_(RB)^(UL), (i.e., RB_(START)=21 to 25), Legacy DMRS is used. As in the caseof specific example 2, as illustrated in FIG. 22, reduced DMRS pattern(1) illustrated in FIG. 21 corresponds to reduced DMRS pattern (1)illustrated in FIG. 4B. Reduced DMRS patterns (2) and (3) are each amethod in which one of two DMRSs included in the legacy DMRS pattern(FIG. 4A) is replaced with data, and DMRSs each having a sequence lengthshorter than an allocated bandwidth are distributedly mapped to theremaining DMRS frequency resource in the SC-FDMA symbol.

As described above, in specific example 3, Legacy DMRS is selected whenthe RIV specifies an RB start position greater than a predeterminedvalue (y₃ in FIGS. 21 and 22), and one DMRS pattern is selected fromamong one or more reduced DMRS patterns when the RIV specifies an RBstart position not greater than the predetermined value.

As described above, PUSCH resource allocation is indicated by the startposition of allocation RB (RB number of the lowest frequency (origin))and the bandwidth from the start position (number of RBs contiguous inthe higher frequency direction) (see, FIG. 16). Accordingly, in orderfor base station 100 to allocate a wide band to terminal 200, basestation 100 needs to indicate an RIV in such a way that start positionRB_(START) corresponds to a low frequency RB number (see, FIG. 22). Inaddition, it is expected that Reduced DMRS is likely to be indicated toterminal 200 having good channel quality and is effective in anenvironment where RB allocation of wider band is performed.

Meanwhile, in variation 3, Reduced DMRS is indicated when RB_(START)corresponds to a low frequency RB number, and Legacy DMRS is indicatedwhen RB_(START) corresponds to a high frequency RB number. According tospecific example 3, base station 100 can perform RB allocation of a wideband to terminal 200 when indicating Reduced DMRS and can also performRB allocation of a narrow band to terminal 200 when indicating LegacyDMRS.

Accordingly, terminal 200 can use Reduced DMRS when allocated RBs of awider band. Thus, it is possible to reduce the overhead of terminal 200in such a good state that a wide band can be allocated, and thereby toachieve higher throughput.

Moreover, in specific example 3, base station 100 can concentrate, inhigh frequency RBs, resource allocation to terminal 200 to which LegacyDMRS is indicated. Thus, interference between a legacy terminal and aterminal capable of Reduced DMRS (terminal allocated low frequency RBs)can be prevented.

(Specific Example 4)

As described above, for PUSCHs of Rel. 11 or before, bandwidth L_(CRBs)that can be indicated by a UL grant is limited to the number of RBsequal to multiple numbers of 2, 3, and 5. Accordingly, some values ofRIV are not indicated in such a case where the bandwidth (L_(CRBs))indicates 7 RBs, for example.

For this reason, in Specific Example 4, base station 100 indicates theuse of Reduced DMRS to terminal 200 using the values of RIV not used inPUSCHs of Rel. 11 or before. Specifically, a plurality of DMRS patternsare associated respectively with the values of RIV corresponding tobandwidths other than the bandwidths allocatable by RIV (i.e.,bandwidths that cannot be allocated).

Specifically, terminal 200 determines one reduced DMRS pattern fromamong one or more reduced DMRS patterns when the MV indicated by basestation 100 has a value other than the number of RBs (bandwidth) equalto a multiple number of 2, 3, and 5.

It should be noted that, whether or not to use Reduced DMRS when the RIVnot used in PUSCHs of Rel. 11 or before is indicated is previouslydetermined or shared between base station 100 and terminal 200 viahigher layer signaling or the like. In addition, the reduced DMRSpatterns specified by MV may be previously determined, or may beindicated to terminal 200 by base station 100 using higher layers or thelike.

In addition, it is assumed that the values of L_(CRBs) and RB_(START) inthe RIV indicating the reduced DMRS patterns are previously indicatedvia higher layer signaling. Alternatively, the values of L_(CRBs) andRB_(START) in the MV indicating the reduced DMRS patterns may be used asL_(CRBs) and RB_(START) identifiable from the values of the RIV andcorresponding to the values of the MV that may be actually indicated. Inthis case, Reduced DMRS indication and flexible scheduling can beachieved simultaneously.

As described above, using the values of RIV not used as allocation RBinformation for DMRS pattern indication make it possible to indicateReduced DMRS to terminal 200 from base station 100 while the flexibilityof frequency scheduling for PUSCHs of Rel. 11 and before.

Embodiment 3

(Summary of Communication System)

A communication system according to Embodiment 3 includes base station100 and one or more terminals 200 as in Embodiment 1 (see, FIG. 6).

However, unlike Embodiment 1, the DPI indicating a DMRS pattern is notused, and a DMRS pattern is indicated by the value of an A-SRS triggerbit (SRS request field) included in a UL grant. Specifically, aplurality of DMRS patterns are associated respectively with the valuesof the existing Aperiodic SRS trigger bit included in controlinformation transmitted from base station 100 to terminal 200.

The A-SRS trigger bit is a bit for indicating A-SRS transmission atpredetermined available transmission timing. Specifically, in Embodiment3, the A-SRS trigger bit indicates the presence or absence of A-SRStransmission request and a DMRS pattern, simultaneously. Stateddifferently, a DMRS pattern is indicated using the existing A-SRStrigger.

More specifically, a plurality of DMRS patterns that may be specifiedare previously indicated to terminal 200, and the DMRS patternscorresponding to the values of A-SRS trigger bit are previouslyindicated to terminal 200. Terminal 200 identifies the A-SRStransmission timing and determines the DMRS pattern corresponding to theA-SRS trigger bit as the DMRS pattern used in the PUSCH subframe, on thebasis of the value of the A-SRS trigger bit indicated by base station100. It should be noted that, the plurality of DMRS patterns that may bespecified, and the DMRS patterns corresponding to the values of A-SRStrigger bit are previously indicated to terminal 200 by base station 100via higher layers or the like, or only predetermined combinations may beused.

The A-SRS transmission timing indicated by an A-SRS trigger bit and theA-SRS transmission timing that can be indicated by a UL grant do nothave to be necessarily the same. For example, the A-SRS transmissiontiming may be commonly used in the entire cell, and the PUSCHtransmission timing may be set to the timing after elapse of apredetermined period of time from reception of a UL grant. Accordingly,SRS interference control between terminals can be easily performed whiledelay in uplink data is minimized.

(Configuration of Base Station 100)

Control section 101 of base station 100 determines PUSCH subframeassignment for terminal 200. Control section 101 section hereindetermines the value of A-SRS trigger bit in consideration of both ofthe presence or absence of an A-SRS transmission request to terminal 200and the DMRS pattern to be indicated to terminal 200.

(Configuration of Terminal 200)

Control section 205 of terminal 200 determines the presence or absenceof A-SRS transmission for the next A-SRS transmission timing on thebasis of the value of A-SRS trigger bit included in the UL grant andindicates the determination result to SRS generating section 209.Moreover, control section 205 determines the DMRS pattern for PUSCHtransmission on the basis of the value of the A-SRS trigger bit.

(Operation)

A description will be provided regarding the operation of base station100 and terminal 200 according to Embodiment 3. The processing flow ofbase station 100 and terminal 200 according to Embodiment 3 issubstantially the same as steps (1) to (4).

However, unlike Embodiment 1, the UL grant includes no DPI in Embodiment3. Instead, base station 100 configures the value of A-SRS trigger biton the basis of the DMRS pattern to be indicated to terminal 200, whileterminal 200 determines the DMRS pattern used in the PUSCH subframe, onthe basis of the value of the A-SRS trigger bit included in the ULgrant.

The number of DMRS patterns selectable by terminal 200 differs dependingon the number of A-SRS trigger bits. FIG. 23A illustrates an example ofDMRS pattern indication used when the number of A-SRS trigger bits isone, while FIG. 23B illustrates an example of DMRS pattern indicationused when the number of A-SRS trigger bits is two.

For example, when the value of A-SRS trigger bit is “0,” no A-SRStransmission request (no trigger) and Legacy DMRS are indicated asillustrated in FIG. 23A (in the case of one bit). When the value ofA-SRS trigger bit is “1,” the presence of A-SRS transmission request andreduced DMRS pattern (1) are indicated.

When the value of A-SRS trigger bit is “00,” no A-SRS transmissionrequest and Legacy DMRS are indicated as illustrated in FIG. 23B (in thecase of two bits). When the value of A-SRS trigger bit is “01,” thepresence of A-SRS transmission request and reduced DMRS pattern (1) areindicated. Likewise, when the value of A-SRS trigger bit is “10,” thepresence of A-SRS transmission request and Legacy DMRS are indicated,and when the value of A-SRS trigger bit is “11,” no A-SRS transmissionrequest and reduced DMRS pattern (2) are indicated.

As described above, an A-SRS transmission request and a DMRS pattern aresimultaneously indicated to terminal 200 by the value of A-SRS triggerbit included in the UL grant. In addition, when the number of A-SRStrigger bits is two or more (see, e.g., FIG. 23B), A-SRSs havingdifferent configurations (1st SRS parameter set and 2nd SRS parameterset in FIG. 23B) and DMRS patterns can be configured in the respectivevalues of the trigger bit. It is assumed that the configurations ofA-SRSs and DMRS parameters corresponding to the respective values of theA-SRS trigger bits can be independently configured.

(Advantageous Effects)

As described above, base station 100 and terminal 200 perform indicationand selection of DMRS patterns through associations between the valuesof A-SRS trigger bit and DMRS patterns.

In LTE, periodic SRS (P-SRS), which is transmitted periodically withoutany trigger bit, is defined. When this P-SRS transmission period isshort, the need for A-SRS transmission requests is supposed to be low.When the need for A-SRS transmission requests is low, base station 100and terminal 200 can use the A-SRS trigger bit for DMRS patternindication bit as in Embodiment 3. As a result, a DMRS pattern suitablefor terminal 200 can be selected from among a plurality of DMRS patternsincluding Legacy DMRS and Reduced DMRS patterns without any increase inoverhead as in Embodiment 1.

Embodiment 4

(Summary of Communication System)

A communication system according to Embodiment 4 includes base station100 and one or more terminals 200 as in Embodiment 1 (see, FIG. 6).

However, unlike Embodiment 1, the DPI indicating a DMRS pattern is notused, and switching between DMRS patterns is performed in accordancewith a downlink control channel (PDCCH or each EPDCCH set) on which a ULgrant is transmitted in Embodiment 4. Specifically, a plurality of DMRSpatterns are associated respectively with a plurality of controlchannels used for transmission of control information to be transmittedto terminal 200 from base station 100.

Specifically, a plurality of DMRS patterns that may be specified arepreviously indicated to terminal 200, and also DMRS patternscorresponding to the control channels (PDCCH or each EPDCCH set) arepreviously indicated to terminal 200. Terminal 200 determines the DMRSpattern corresponding to the control channel used for transmission of aUL grant indicated by base station 100, as the DMRS pattern used in thetransmission of PUSCH subframe. Incidentally, the plurality of DMRSpatterns that may be specified, and the DMRS patterns corresponding tothe control channels may be previously indicated to terminal 200 by basestation 100 via higher layers, or only predetermined combinations may beused.

(Configuration of Base Station 100)

Specifically, control section 101 of base station 100 determines PUSCHsubframe assignment for terminal 200. Control section 101 hereindetermines mapping of a control signal in consideration of both of acontrol channel (PDCCH and EPDCCH set) to which the control signal forterminal 200 (including a UL grant) is mapped, and the DMRS pattern tobe indicated to terminal 200.

(Configuration of Terminal 200)

Control section 205 of terminal 200 determines the DMRS pattern forPUSCH transmission according to whether the control channel on which theUL grant is transmitted is a PDCCH or EPDCCH set.

(Operation)

A description will be provided regarding the operation of base station100 and terminal 200 according to Embodiment 2. The processing flow ofbase station 100 and terminal 200 is substantially the same as steps (1)to (4).

However, unlike Embodiment 1, the UL grant includes no DPI. Instead,base station 100 configures the control channel used for transmission ofa UL grant on the basis of a DMRS pattern to be indicated to terminal200, and terminal 200 determines the DMRS pattern used in the PUSCHsubframe on the basis of the control channel (PDCCH or EPDCCH set) usedfor the transmission of UL grant.

It should be noted that, regarding the configuration of an EPDCCH set,only one or more than one EPDCCH set may be configured. FIG. 24illustrates an example of DMRS pattern indication used when a PDCCH andthree EPDCCH sets are configured.

In FIG. 24, terminal 200 blind-decodes three types of EPDCCH sets inaddition to a PDCCH. Terminal 200 determines, according to in whichcontrol channel the UL grant is successfully decoded, the DMRS patternin the PUSCH transmission indicated by the UL grant.

As illustrated in FIG. 24, when a UL grant is transmitted using a PDCCHor EPDCCH set 1, terminal 200 determines that Legacy DMRS is indicated.When a UL grant is transmitted using EPDCCH set 2, terminal 200determines that reduced DMRS pattern (1) is indicated, and when a ULgrant is transmitted using EPDCCH set 3, terminal 200 determines thatReduced DMRS pattern (2) is indicated.

(Advantageous Effects)

As described above, base station 100 and terminal 200 perform indicationand selection of DMRS patterns through associations between the controlchannels on which a UL grant is transmitted, and DMRS patterns.

Macro cell base stations are likely to use PDCCHs for transmission of aUL grant because PDCCHs provide a wide coverage and are supported byterminals compliant with existing standard (Rel. 8), Meanwhile,regarding EPDCCHs, a plurality of EPDCCH sets (two EPDCCH sets in Rel.11) can be configured as blind-decoding targets. Accordingly, suchoperation may be possible in which a macro cell base station and a smallcell base station are associated with different EPDCCH sets, and a ULgrant is transmitted from a different base station according to theconditions of terminal 200. As described herein, the operation is whicha different control channel (or different EPDCCH set) is configured foreach of a plurality of base stations (or transmission/reception points)capable of communicating with terminal 200 may be possible.

For example, such operation is possible in which a PDCCH and EPDCCH set1 are used for transmission of a UL grant from a macro cell basestation, which has a wide coverage and is highly reliable, and EPDCCHsets 2 and 3 are used for transmission of a UL grant from a small cellbase station located near terminal 200. In this operation, the controlchannels (PDCCH and EPDCCH set 1) used for transmission of a UL grant bya macro cell base station are associated with a legacy DMRS pattern,while the control channels (EPDCCH sets 2 and 3) used for transmissionof a UL grant by a small cell base station is associated with reducedDMRS patterns.

As described above, associating the control channels used fortransmission of a UL grant with DMRS patterns makes it possible toachieve operation which allows terminal 200 to use Reduced DMRS incommunication with a specific base station (transmission and receptionpoint). Accordingly, switching between DMRS patterns is made possiblewithout any increase in overhead and without adding any restrictions tothe control bits included in a UL grant.

Embodiment 5

(Summary of Communication System)

A communication system according to Embodiment 5 includes base station100 and one or more terminals 200 as in Embodiment 1 (see, FIG. 6).

However, unlike Embodiment 1, the DPI indicating a DMRS pattern is notused, but the value of cyclic shift indication bit (CS field (or cyclicshift indicator)) included in a UL grant is used to indicate a DMRSpattern in Embodiment 5. Specifically, a plurality of DMRS patterns areassociated respectively with the values of the existing CS fieldincluded in control information to be transmitted to terminal 200 frombase station 100.

The CS field is a bit indicated by a UL grant and used to indicate acyclic shift value and the OCC index of an OCC applied to a DMRS forPUSCH transmission. Specifically, the CS field indicates a cyclic shiftvalue and the OCC index of an OCC applied to a DMRS and a DMRS patternsimultaneously. Stated differently, the DMRS pattern is indicated usingthe existing CS field.

Specifically, a plurality of DMRS patterns that may be specified arepreviously indicated to terminal 200, and the DMRS patternscorresponding to the values of CS field are previously indicated toterminal 200. Terminal 200 identifies the cyclic shift value and OCCindex and determines the DMRS pattern corresponding to the CS field asthe DMRS pattern used in the PUSCH subframe, on the basis of the CSfield value indicated by base station 100. It should be noted that, theplurality of DMRS patterns that may be specified, and the DMRS patternscorresponding to the values of CS field are previously indicated toterminal 200 by base station 100 via higher layers or the like, or onlypredetermined combinations may be used.

(Configuration of Base Station 100)

Control section 101 of base station 100 determines PUSCH subframeassignment for terminal 200. Control section 101 herein determines thevalue of CS field in consideration of the cyclic shift value and OCCindex for the DMRS of terminal 200, and the DMRS pattern to be indicatedto terminal 200.

(Configuration of Terminal 200)

Control section 205 of terminal 200 identifies the cyclic shift valueand OCC index for the DMRS on the basis of the value of CS fieldincluded in the UL grant and indicates the information to DMRSgenerating section 208. Moreover, control section 205 determines theDMRS pattern for PUSCH transmission on the basis of the value of CSfield and indicates the DMRS pattern to DMRS generating section 208.

(Operation)

A description will be provided regarding the operation of base station100 and terminal 200 according to Embodiment 5. The processing flow ofbase station 100 and terminal 200 is substantially the same as steps (1)to (4).

However, unlike Embodiment 1, the UL grant includes no DPI in Embodiment5. Instead, base station 100 configures the value of CS field on thebasis of the DMRS pattern to be indicated to terminal 200, and terminal200 determines the DMRS pattern used in the PUSCH subframe on the basisof the value of CS field included in the UL grant.

FIG. 25 illustrates an example of DMRS pattern indication using the CSfield (3 bits). In FIG. 25, λ represents a layer number. In addition,the cyclic shift value that can be indicated using the CS field is 0 to11, and the OCC index is 0 and 1. OCC index 0 corresponds to [+1 +1],and OCC index 1 corresponds to [+1 −1].

As illustrated in FIG. 25, the values of CS field 000, 010, and 111 areassociated with Legacy DMRS, and the values of CS field 011 and 100 areassociated with reduced DMRS pattern (1) while the values of CS field101 and 110 are associated with reduced DMRS pattern (2).

(Advantageous Effects)

As described above, base station 100 and terminal 200 perform indicationand selection of DMRS patterns through associations between the valuesof CS field and DMRS patterns.

As described above, Reduced DMRS is likely to be used when terminal 200is connected to a small cell base station and when the channel qualityof terminal 200 is sufficiently good. It is assumed that the number ofterminals in such a situation is small and that interference to anothercell is low in such a situation. In other words, Reduced DMRS is likelyto be used in a situation where the need for orthogonalization using CSand OCCs and interference control is low. Accordingly, although certainrestrictions are imposed on indication of CS/OCCs because a DMRS patternis indicated simultaneously with CS/OCCs using the CS field, there isalmost no influence of drawback due to the restrictions, and switchingbetween DMRS patterns can be appropriately performed. In addition, sinceDMRS patterns are indicated using the existing CS field, there is noincrease in overhead because of no additional bits.

In Embodiment 5, application of a DMRS pattern other than Legacy DMRS(i.e., application of reduced DMRS patterns) may be limited to a casewhere the number of layers (transmission rank) is equal to one (i.e.,λ=0). Specifically, when the number of layers (transmission rank) isequal to one, terminal 200 (control section 205) determines a specificDMRS pattern to be used by terminal 200, on the basis of the CS field,and when the number of layers (transmission rank) is at least two,terminal 200 determines the legacy DMRS pattern as the specific DMRSpattern to be used by terminal 200 regardless of the value of CS field.

FIG. 26 illustrates a case where application of reduced DMRS patterns islimited to λ=0 (number of layers equal to one). In FIG. 26, when thenumber of layers is one (λ=0), the reduced DMRS pattern associated withthe CS field is used, but when the number of layers is at least 2 (λ=1to 3), Legacy DMRS is used instead of the reduced DMRS patternassociated with the CS field.

When the number of layers is large, simultaneous transmission(multiplexing) of a plurality of pieces of data from different layersusing the same time and frequency resources makes it possible to achievehigher throughput. In this transmission, a DMRS is also multiplexed, sothat it is likely to be affected by a channel estimation error.Accordingly, when the number of layers is large, further improvement inthroughput can be expected by using Reduced DMRS as in the case wherethe number of layers is one, but correctly receiving data withoutretransmission by performing accurate channel estimation is morepreferable to slight improvement in resource efficiency obtained by useof Reduced DMRS. In addition, when the number of layers is large, a highdata rate is achievable without relying on Reduced DMRS. Accordingly, asillustrated in FIG. 26, switching between DMRS patterns in accordancewith the number of layers allows an appropriate DMRS in accordance withthe number of layers to be used.

It should be noted that, changing a DMRS in accordance with a searchspace on which format of a UL grant is transmitted can achieve theadvantageous effects obtained in Embodiment 5. For example, a UL grantincludes DCI format 0, which indicates single-layer transmission, andDCI format 4, which is capable of indicating at least two-layertransmission. Accordingly, it is possible to employ a configuration inwhich Legacy DMRS is used regardless of the value of CS field for a ULgrant indicating single-layer transmission (e.g., DCI format 0), whileReduced DMRS is used with some values of the CS field for a UL grant(e.g., DCI format 4), which is capable of indicating at least two-layertransmission. Alternatively, control channels used for transmitting a ULgrant include a common search space (CSS), which indicates single-layertransmission, and a UE-specific search space (USS), which is capable ofindicating at least two-layer transmission. Accordingly, Legacy DMRS maybe used regardless of the value of CS field for common search space(CSS), which indicates single-layer transmission, while Reduced DMRS maybe used with some values of the CS field for a UE-specific search space(USS), which is capable of indicating at least two-layer transmission.

Embodiment 6

A communication system according to Embodiment 6 includes base station100 and one or more terminals 200 as in Embodiment 1 (see, FIG. 6).

However, unlike Embodiment 1, the DPI indicating a DMRS pattern is notincluded in a UL grant, but is transmitted as a control signal differentfrom the UL grant on a control channel.

In the following description, a control signal for a DPI consisting oftwo bits is called DCI format 3d, while a control signal for a DPIconsisting of one bit is called DCI format 3dA.

Specifically, base station 100 transmits DCI format 3d or DCI format 3dAas a DPI. Meanwhile, terminal 200 blind-decodes each DCI format 3d/3dA,and when successfully decoding DCI format 3d/3dA and finding a DPI inthe format, terminal 200 uses the DMRS pattern indicated by the DPI.

Base station 100 previously indicates use of DCI format 3d/3dA and theDMRS patterns that may be specified by a DPI of DCI format 3d/3dA toterminal 200. In addition, base station 100 previously indicates apseudo terminal-ID required for decoding DCI format 3d/3dA to terminal200. The pseudo terminal-ID may be a value shared among a plurality ofterminals 200. Base station 100 transmits DCI format 3d/3dA with a ULgrant. The transmitted DCI format 3d/3dA includes a DPI intended for oneor more terminals 200, and CRC bits masked by a pseudo terminal-ID areadded. To put it differently, the control signal transmitted from basestation 100 to terminal 200 includes a DPI and UL grant, and masking(scrambling) different from masking applied to the UL grant is appliedto the DPI.

Terminal 200 blind-decodes the DCI format 3d/3dA in addition to the ULgrant. During the blind-decoding, terminal 200 uses the CRC masked usingthe terminal ID of terminal 200 to determine success or failure ofdecoding the UL grant, and uses the CRC masked using the pseudoterminal-ID to determine success or failure of decoding the DCI format3d/3dA. Upon succeeding in decoding the UL grant and DCI format 3d/3dAat the same time, terminal 200 selects the DMRS pattern according to thevalue of DPI intended for terminal 200 included in DCI format 3d/3dA andtransmits a PUSCH assigned by the UL grant.

Base station 100 receives the PUSCH transmitted by terminal 200 anddecodes the PUSCH. It should be noted that, since base station 100cannot determine whether DCI format 3d/3dA has been correctly decoded byterminal 200, base station 100 sequentially decodes PUSCH while assumingthat the PUSCH is transmitted using any of Legacy DMRS and the DMRSpatterns indicated by the DPI.

As described, in Embodiment 6, a DPI is transmitted and received using acontrol signal (DCI format 3d/3dA) to which scrambling different fromthat applied to a UL grant is applied, and switching between DMRSpatterns is performed in accordance with the value of DPI.

As described above, while a UL grant in Rel. 11 or before is usedwithout any change, Reduced DMRS can be indicated using a differentcontrol signal. Thus, base station 100 can perform operation using ascheduler of Rel. 11 or before for terminals using Legacy DMRS andindicate a DMRS pattern, using an independent control signal, only toterminals using Reduced DMRS. Specifically, adding the features of DCIformat 3d/3dA to the scheduler of conventional base station 100 alonemakes it possible to indicate Reduced DMRS. As a result, implementationof base station 100 becomes easy.

Incidentally, when terminal 200 uses Reduced DMRS, a large amount oftransmission data is transmitted as compared with when terminal 200 usesLegacy DMRS. When using Reduced DMRS, terminal 200 can perform mappingof transmission data in the same manner as when terminal 200 uses LegacyDMRS (i.e., maps no transmission data to resources that have becomeunused because of Reduced DMRS) and then maps the remaining transmissiondata to the resources that have become unused because of Reduced DMRS.FIG. 27 illustrates an example of this data mapping sequence. WhenReduced DMRS is used, the amount of transmission data is determined inaccordance with the DMRS pattern. In this case, as illustrated in FIG.27, data is first mapped to the top of a subframe as in Legacy DMRS.Some transmission data remains unmapped because of application ofReduced DMRS. Accordingly, the remaining unmapped data is mapped lastlyto the resources that have become unused because of Reduced DMRS.

With this configuration, the data mapping sequence in the resourcesother than the resources to which data is newly mapped because ofReduced DMRS (i.e., resources that have become unused because of ReducedDMRS) is identical to the data mapping sequence when Legacy DMRS isused. Thus, even when base station 100 cannot determine whether or notterminal 200 has successfully decoded DCI format 3d/3dA (i.e., cannotdetermine whether it is Legacy DMRS or non-Legacy DMRS), base station100 no longer has to decode data according to a plurality of datamapping sequences in consideration of a plurality of different datamapping patterns. In addition, even when terminal 200 transmits a PUSCHwith a legacy DMRS pattern, there is a possibility that base station 100can correctly decode the data in a data mapping sequence assumingReduced DMRS. Thus, the configuration of receiver in base station 100can be simplified and processing delay in decoding can be shortened.

The embodiments of the present disclosure have been described above.

(Additional Embodiments)

[1] When the transmission timing of ACK/NACK response signal fordownlink data and the transmission timing of a PUSCH indicated by a ULgrant are the same, the ACK/NACK response signal is replaced with datain a PUSCH subframe. Since this ACK/NACK response signal is required tohave high judgment accuracy (low error rate), it is defined that anACK/NACK response signal is mapped to an SC-FDMA symbol adjacent to aDMRS in Rel. 11 or before. Meanwhile, when Reduced DMRS is used, DMRSsare partially replaced with data. Accordingly, there arises apossibility that an ACK/NACK response signal cannot be mapped to anSC-FDMA symbol adjacent to a DMRS, which results in failure of ensuringchannel estimation accuracy with respect to the judgment of the ACK/NACKresponse signal. FIGS. 28A and 28B illustrate examples of how ACK/NACKresponse signals are mapped in Legacy DMRS (see, FIG. 28A) and inReduced DMRS (see, FIG. 28B) in a PUSCH. For example, reduce DMRSpattern (1) illustrated in FIG. 4B is used in FIG. 28B, and it ispossible to observe that the ACK/NACK response signals are mapped to thepositions away from the DMRS.

Accordingly, when an ACK/NACK response signal is multiplexed on a PUSCH,terminal 200 may be configured to always use Legacy DMRS even if ReducedDMRS is indicated. With this configuration, the channel estimationaccuracy with respect to the judgment of ACK/NACK response signals canbe kept at the same level in Rel. 11 and before.

Alternatively, Reduced DMRS usable when an ACK/NACK response signal ismultiplexed on a PUSCH may be limited to a pattern in which a DMRS ismapped to an SC-FDMA symbol adjacent to an ACK/NACK response signal. Thepattern in which a DMRS is mapped to an SC-FDMA symbol adjacent to anACK/NACK response signal is reduced DMRS pattern (3) illustrated in FIG.4D, for example. With this configuration, degradation of channelestimation accuracy with respect to the judgment of ACK/NACK responsesignals can be minimized.

Alternatively, when Reduced DMRS is used, the mapping positions ofACK/NACK response signals may be changed. In the example illustrated inFIG. 28B, for example, the ACK/NACK response signals may be mappedconcentratedly to positions near the remaining DMRS in Reduced DMRS. Asa result, Reduced DMRS can be flexibly used while the channel estimationaccuracy with respect to the judgment of ACK/NACK response signals canbe ensured.

[2] The above-noted embodiments have been described by examples ofhardware implementations, but the present disclosure can be alsoimplemented by software in conjunction with hardware.

In addition, the functional blocks used in the descriptions of theembodiments are typically implemented as LSI devices, which areintegrated circuits. The functional blocks may be formed as individualchips, or a part or all of the functional blocks may be integrated intoa single chip. The term “LSI” is used herein, but the terms “IC,”“system LSI,” “super LSI” or “ultra LSI” may be used as well dependingon the level of integration.

In addition, the circuit integration is not limited to LSI and may beachieved by dedicated circuitry or a general-purpose processor otherthan an LSI. After fabrication of LSI, a field programmable gate array(FPGA), which is programmable, or a reconfigurable processor whichallows reconfiguration of connections and settings of circuit cells inLSI may be used.

Should a circuit integration technology replacing LSI appear as a resultof advancements in semiconductor technology or other technologiesderived from the technology, the functional blocks could be integratedusing such a technology. Another possibility is the application ofbiotechnology and/or the like.

A terminal according to an aspect of this disclosure includes: areception section that receives uplink control information; a controlsection that determines a specific mapping pattern based on the controlinformation from among a plurality of mapping patterns for an uplinkdemodulation reference signal (DMRS); and a generation section thatgenerates a DMRS according to the specific mapping pattern.

In the terminal according to an aspect of this disclosure, the controlinformation includes information indicating the specific mappingpattern.

In the terminal according to an aspect of this disclosure, theinformation indicating the specific mapping pattern indicates thespecific mapping pattern and a virtual cell ID.

In the terminal according to an aspect of this disclosure: the pluralityof mapping patterns are associated respectively with values of uplinkallocation information included in the control information; and thecontrol section determines a mapping pattern corresponding to thereceived assignment information as the specific mapping pattern.

In the terminal according to an aspect of this disclosure: the pluralityof mapping patterns include a first mapping pattern and a second mappingpattern that includes a smaller amount of resource to which a DMRS ismapped than the first mapping pattern; the allocation informationindicating an odd number of allocation resource blocks is associatedwith the first mapping pattern; and the allocation informationindicating an even number of allocation resource blocks is associatedwith the second mapping pattern.

In the terminal according to an aspect of this disclosure: the pluralityof mapping patterns include a first mapping pattern and a second mappingpattern that includes a smaller amount of resource to which a DMRS ismapped than the first mapping pattern; the allocation informationindicating an odd number of allocation resource blocks is associatedwith the number of allocation resource blocks equal to the odd numberplus or minus one and the second mapping pattern; and the allocationinformation indicating an even number of resource blocks is associatedwith allocation of the even number of resource blocks and the firstmapping pattern.

The terminal according to an aspect of this disclosure: the plurality ofmapping patterns include a first mapping pattern and a second mappingpattern that includes a smaller amount of resource to which a DMRS ismapped than the first mapping pattern; the allocation informationindicating an allocation bandwidth equal to or less than a predeterminedvalue is associated with the first mapping pattern; and the allocationinformation indicating an allocation bandwidth greater than thepredetermined value is associated with the second mapping pattern.

The terminal according to an aspect of this disclosure: the plurality ofmapping patterns include a first mapping pattern and a second mappingpattern that includes a smaller amount of resource to which a DMRS ismapped than the first mapping pattern; the allocation informationindicating that the lowest frequency of an allocation band is greaterthan a predetermined value is associated with the first mapping pattern;and the allocation information indicating that the lowest frequency ofan allocation band is equal to or less than the predetermined value isassociated with the second mapping pattern.

In the terminal according to an aspect of this disclosure, the pluralityof mapping patterns are associated respectively with values of theallocation information corresponding to bandwidths other than abandwidth allocatable by the allocation information.

In the terminal according to an aspect of this disclosure: the pluralityof mapping patterns are associated respectively with values of AperiodicSRS trigger included in the control information; and the control sectiondetermines a mapping pattern corresponding to the received Aperiodic SRStrigger, as the specific mapping pattern.

In the terminal according to an aspect of this disclosure: the pluralityof mapping patterns are associated respectively with a plurality ofcontrol channels used for transmission of the control information; andthe control section determines a mapping pattern corresponding to acontrol channel that has been used for transmission of the controlinformation, as the specific mapping pattern.

In the terminal according to an aspect of this disclosure: the pluralityof mapping patterns include a first mapping pattern and a second mappingpattern that includes a smaller amount of resource to which a DMRS ismapped than the first mapping pattern; a control channel used fortransmission of the control information by a macro cell base station isassociated with the first mapping pattern; and a control channel usedfor transmission of the control information by a small cell base stationis associated with the second mapping pattern.

In the terminal according to an aspect of this disclosure: the pluralityof mapping patterns are associated respectively with values of a cyclicshift indicator that is included in the control information and thatindicates a cyclic shift value and an orthogonal cover code; and thecontrol section determines a mapping pattern corresponding to thereceived cyclic shift indicator, as the specific mapping pattern.

In the terminal according to an aspect of this disclosure: the pluralityof mapping patterns include a first mapping pattern and a second mappingpattern that includes a smaller amount of resource to which a DMRS ismapped than the first mapping pattern; the control section determines amapping pattern corresponding to the received cyclic shift indicator asthe specific mapping pattern when transmission rank is one; and thecontrol section determines the first mapping pattern as the specificmapping pattern when transmission rank is two or greater.

In the terminal according to an aspect of this disclosure: the controlinformation includes information indicating the specific mapping patternand uplink allocation information; and the information indicating thespecific mapping pattern is subjected to scrambling different fromscrambling used for the allocation information.

A base station according to an aspect of this disclosure includes: acontrol signal generating section that generates uplink controlinformation based on a mapping pattern to be indicated to a terminalfrom among a plurality of mapping patterns for an uplink demodulationreference signal (DMRS); and a transmission section that transmits thegenerated control information.

A method of generating a demodulation reference signal (DMRS), accordingto an aspect of this disclosure includes: receiving uplink controlinformation; determining a specific mapping pattern based on the controlinformation from among a plurality of mapping patterns for an uplinkDMRS; and generating a DMRS according to the specific mapping pattern.

A transmission method according to an aspect of this disclosureincludes: generating uplink control information based on a mappingpattern to be indicated to a terminal from among a plurality of mappingpatterns for an uplink demodulation reference signal (DMRS); andtransmitting the generated control information.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to mobile communication systems.

Reference Signs List 100 Base station 200 Terminal  11 Control signalgenerating section 12, 25 Transmission section 13, 21 Reception section14, 114 Channel estimating section  15 Reception signal processingsection 101, 23, 205 Control section 102 Control information generatingsection 103, 206 Coding section 104, 207 Modulation section 105, 212Mapping section 106, 213 IFFT section 107, 214 CP adding section 108,215 Radio transmitting section 109, 201 Radio receiving section 110, 202CP removing section 111, 203 FFT section 112 Demapping section 113 CSImeasuring section 115 Equalization section 116 IDFT section 117Demodulation section 118 Decoding section 119 Determination section 22,204 Control signal extracting section 24, 208 DMRS generating section209 SRS generating section 210 Multiplexing section 211 DFT section

1. A terminal comprising: a receiver, which, in operation, receivescontrol information which is used for scheduling of a PUSCH (PhysicalUplink Shared Channel) and which includes information for determining amapping pattern of an uplink DMRS (Demodulation Reference Signal) toresource elements; circuitry, which is coupled to the receiver andwhich, in operation, maps the uplink DMRS to the resource elements basedon the information; and a transmitter, which is coupled to the circuitryand which, in operation, transmits the mapped uplink DMRS, wherein themapping pattern is determined out of a plurality of mapping patternsbased on the information, and the plurality of mapping patterns includeat least two mapping patterns in which numbers of symbols, to which theuplink DMRS is mapped, are different.
 2. The terminal according to claim1, wherein the plurality of mapping patterns include at least twomapping patterns in which numbers of resource elements, to which theuplink DMRS is mapped, are different.
 3. The terminal according to claim1, wherein the plurality of mapping patterns include at least twomapping patterns in which numbers of symbols of a slot or a subframe, towhich the uplink DMRS is mapped, are different.
 4. The terminalaccording to claim 1, wherein the plurality of mapping patterns includea mapping pattern in which a number of resources, to which the uplinkDMRS is mapped, is less than a number of resources to which an uplinkDMRS in LTE-A Release 11 is mapped.
 5. The terminal according to claim1, wherein the plurality of mapping patterns are signaled by ahigher-layer.
 6. The terminal according to claim 1, wherein theplurality of mapping patterns include a mapping pattern that maps theuplink DMRS having a sequence length less than a frequency bandwidth, towhich the PUSCH is assigned.
 7. The terminal according to claim 1,wherein the plurality of mapping patterns respectively correspond toeither a hopping is enabled or disabled.
 8. The terminal according toclaim 1, wherein the control information includes information fordetermining a cyclic shift and an orthogonal sequence, and thecircuitry, in operation, generates the uplink DMRS based on thedetermined cyclic shift and the determined orthogonal sequence.
 9. Theterminal according to claim 1, wherein when transmitting ACK/NACKmultiplexed with the PUSCH, the circuitry maps the ACK/NACK adjacent tothe mapped uplink DMRS.
 10. A communication method comprising: receivingcontrol information which is used for scheduling of a PUSCH (PhysicalUplink Shared Channel) and which includes information for determining amapping of an uplink DMRS (Demodulation Reference Signal) to resourceelements; mapping the uplink DMRS to the resource elements based on theinformation; and transmitting the mapped uplink DMRS, wherein themapping pattern is determined out of a plurality of mapping patternsbased on the information, and the plurality of mapping patterns includeat least two mapping patterns in which numbers of symbols, to which theuplink DMRS is mapped, are different.
 11. The communication methodaccording to claim 10, wherein the plurality of mapping patterns includeat least two mapping patterns in which numbers of resource elements, towhich the uplink DMRS is mapped, are different.
 12. The communicationmethod according to claim 10, wherein the plurality of mapping patternsinclude at least two mapping patterns in which numbers of symbols of aslot or a subframe, to which the uplink DMRS is mapped, are different.13. The communication method according to claim 10, wherein theplurality of mapping patterns include a mapping pattern in which anumber of resources, to which the uplink DMRS is mapped, is less than anumber of resources to which an uplink DMRS in LTE-A Release 11 ismapped.
 14. The communication method according to claim 10, wherein theplurality of mapping patterns are signaled by a higher-layer.
 15. Thecommunication method according to claim 10, wherein the plurality ofmapping patterns include a mapping pattern that maps the uplink DMRShaving a sequence length less than a frequency bandwidth, to which thePUSCH is assigned.
 16. The communication method according to claim 10,wherein the plurality of mapping patterns respectively correspond toeither a hopping is enabled or disabled.
 17. The communication methodaccording to claim 10, wherein the control information includesinformation for determining a cyclic shift and an orthogonal sequence,and the uplink DMRS is generated based on the determined cyclic shiftand the determined orthogonal sequence.
 18. The communication methodaccording to claim 10, wherein when transmitting ACK/NACK multiplexedwith the PUSCH, the ACK/NACK is mapped adjacent to the uplink DMRS.